Dairy foods are a probable cause of premature death

What is covered in this review:

Dairy foods are widely recommended to promote health but have been associated with an increased risk of premature death when substituted for healthful plant-based alternatives.
Meta-analyses of prospective cohort studies found that substituting whole grains, legumes, and nuts with a 200-245 g/day serving of dairy foods, including yogurt, was associated with between a 12% and 28% increased risk of all-cause mortality.
A meta-analysis of Mendelian randomization studies involving 119,787 participants presented here found that a genetically predicted 1% increment in energy from total dairy was causally associated with an 8% increased risk of all-cause mortality compared to other typically consumed foods (Figure 1).
Genetically predicted dairy intake was causally associated with a 44% increased risk of all-cause mortality in a subgroup analysis in which dairy foods likely predominantly displaced healthful plant foods.
A meta-analysis of prospective cohort studies involving 618,142 participants presented here found that substituting 6% of energy from plant protein with dairy protein was associated with an 18% increased risk of all-cause mortality (Figure 2).
A prospective cohort study with 8.1 million person-years of follow-up found that substituting 5% of energy from total plant fat and fat from grains with dairy fat was associated with a 9% and 20% increased risk of all-cause mortality, respectively.
A pooled analysis of 3 Harvard prospective cohort studies found that substituting each 10 g/day serving of plant oils with butter was associated with a 21% increased risk of all-cause mortality.
A meta-analysis of prospective cohort studies commissioned by the World Health Organization found that substituting 5% of energy from carbohydrate, monounsaturated fat, or polyunsaturated fat with saturated fat was associated with between a 9% and 19% increased risk of all-cause mortality.
A meta-analysis of prospective cohort studies involving 730,635 participants presented here found that substituting ≤5% of energy from carbohydrate or plant-derived monounsaturated fat with animal-derived monounsaturated fat was associated with between a 12% and 31% increased risk of all-cause mortality (Figure 3).
A meta-analysis of randomized controlled trials involving 55,267 participants presented here found that substituting saturated fat primarily with carbohydrate or polyunsaturated fat and reducing dietary cholesterol reduces the odds of all-cause mortality by 26% per 1 mmol/L reduction in total cholesterol for 5 years of cumulative exposure (Figure 4).
A meta-analysis of 14 prospective cohort studies found that each 100 mg/day increment in dietary cholesterol intake was associated with a 6% increased risk of all-cause mortality.
A Mendelian randomization study found that higher circulating calcium was causally associated with 28% lower odds of longevity per 0.09–0.12 mmol/L increment in circulating calcium, a change comparable to that found for supplementation of 1,000 mg/day calcium.
Evidence from >100 prospective cohort studies found that a high intake of fiber and plant-derived antioxidants were associated with up to a 32% decreased risk of all-cause mortality, corroborating evidence of a benefit of substituting dairy with healthful plant foods (Table 1).
The benefit of substituting healthful plant foods with dairy on reducing the risk of premature death may be mediated by intermediate risk factors, including Apolipoprotein B (ApoB), blood pressure, flow-mediated dilation (FMD), inflammation, body fat, and insulin-like growth factor-1 (IGF-1).
Evidence from >1,000 controlled dietary experiments have established that substituting dairy foods with healthful plant foods and the associated nutrients reduces atherogenic blood lipids, including ApoB, the primary lipid determinant of all-cause mortality.
A meta-analysis of 104 controlled feeding experiments found that substituting equal parts of energy from carbohydrate, monounsaturated fat, and polyunsaturated fat with 5% of energy from saturated fat increases ApoB by 37 mg/dL, predicting a 36% increased risk of all-cause mortality for 4.7 years of cumulative exposure.
Evidence from >200 randomized controlled trials indicate that substituting dairy foods with healthful plant foods reduces systolic and diastolic blood pressure.
A meta-analysis of 5 randomized controlled trials found that substituting 2 cups per day of ultra-processed or unsweetened soy milk with low fat dairy milk increases systolic blood pressure by 8 mmHg, predicting a 12% increased risk of all-cause mortality for 3.8 years of cumulative exposure.
Evidence from >50 controlled feeding experiments found that dairy fat reduces postprandial and fasting FMD, predicting up to a 77% increased risk of all-cause mortality.
Evidence from >130 randomized controlled trials indicate that substituting dairy foods with healthful plant foods reduces inflammation.
Clinical and genetic evidence indicates that long-term dairy intake causes weight gain compared to other typically consumed foods.
Evidence from >20 randomized controlled trials found that milk and whey intake increase IGF-1 compared to other typically consumed foods.
Meta-analyses of epidemiological studies and Mendelian randomization studies demonstrate no benefit of dairy on fracture risk compared to other typically consumed foods, but that saturated animal fat likely increases risk.
Prospective cohort studies have found that dairy is associated with an increased risk of cardiovascular disease, breast and total cancer, and frailty compared to healthful plant foods, and prostate cancer, ovarian cancer, and Parkinson’s disease compared to even non-specific, typically unhealthy foods.
A meta-analysis of Mendelian randomization studies involving 435,707 participants presented here found that a genetically predicted single serving per day increment in total dairy intake was causally associated with a 107% increased risk of Parkinson’s disease compared to other typically consumed foods (Figure 5).
Nomadic pastoralist populations that subsisted chiefly on large quantities of grass-fed meat and raw milk had high rates of obesity, atherosclerotic cardiovascular disease, rheumatoid arthritis, gout, habitual constipation, and erectile dysfunction.

Dairy foods, and in particular cow’s milk are recommended by many health organizations to improve overall health, but leading health experts have raised serious concerns over the quality of the foods substituted for dairy in many studies that have likely played an important role in the development of these recommendations.¹ Two recent meta-analyses of prospective cohort studies have raised further concerns due to the finding that substituting healthful plant foods with dairy was associated with an increased risk of all-cause mortality.² ³ Moreover, risk estimates for a single serving per day increment in dairy were generally comparable to adverse lifestyle exposures discouraged by major health organizations, including the 18% to 22% increased risk observed in meta-analyses for passive smoking, smokeless tobacco use, and high volume alcohol drinking (45 to 64 g/day ethanol).⁴ ⁵ ⁶ Not only is all-cause mortality perhaps the most important outcome of interest in the study of health, it can often be more informative than specific disease outcomes as competing risk of death from other causes can obscure or even reverse the true relationship with an outcome of interest.⁷ This may be particularly the case for diet which has been observed to have a uniform effect across multiple major causes of death.⁸ This review will examine the evidence of the effect of substituting dairy with healthful alternatives and the risk of all-cause mortality and the underlying mechanisms which may explain this relationship.

As a higher intake of one food implies a lower intake of other foods to maintain energy balance, the effect that dairy foods have on health outcomes can normally only be elucidated by the foods being displaced.¹ However, given that ultra-processed foods now contribute to more than 50% of energy of the diets in Western populations,⁹ ¹⁰ and fast approaching these levels in Asian populations,¹¹ ¹² studies examining the effect of dairy on health outcomes will likely be complicated due to comparisons being primarily to such foods. Indeed, epidemiological and genetic evidence indicates that soft drinks and meat, but not vegetables, legumes, and nuts are a major sources of energy that displaces milk.¹³ ¹⁴ ¹⁵ Thus, dairy foods likely primarily displace ultra-processed and other animal foods in most studies, and the failure to recognize this limitation in the conclusions of many studies has likely contributed to the public’s confusion surrounding dairy and health.

Two recent meta-analyses of prospective cohort studies found that substituting dairy foods with healthful plant foods, but not other animal foods were associated with a decreased risk of all-cause mortality. One meta-analysis of 4 cohorts indicated that substituting each equivalent serving of legumes or nuts with a 200 g/day serving of dairy foods was associated with between a 20% and 28% increased risk of all-cause mortality.² Another meta-analysis of 2 cohorts indicated that substituting each 28 g/day serving of whole grains or nuts with a 245 g/day serving of yogurt was associated with a 12% and 28% increased risk of all-cause mortality, respectively, and that the risk for milk and cheese is even higher.³ It may be important to recognize that the included studies defined whole grains as foods containing as little as 25% whole grain or bran content while separately finding that each 4 g/day increase in cereal fiber intake was associated with a 16% reduced risk of all-cause mortality.⁸ ¹⁶ Thus, a stricter definition of whole grain intake may have resulted in a stronger association. A strength of these meta-analyses is that the estimates were largely derived from studies that used repeated dietary assessments throughout more than 25 years of follow-up, and controlled for medical history, lifestyle factors, and diet quality.¹⁷ ¹⁸ Nevertheless, residual confounding cannot be entirely excluded, although the replication of the findings of an increased risk for dairy foods associated with a healthy lifestyle, including yogurt provides confidence in these findings.

Mendelian randomization (MR) is an approach that uses genetic variants to explore a causal relationship between environmental exposures and health outcomes.¹⁹ However, in the study of diet MR studies will typically suffer from the same limitation evident in epidemiological studies in that the source of energy of interest will be primarily displacing animal and ultra-processed foods. This limitation may be demonstrated by a MR study that investigated the participants in the PREDIMED dietary trial. This study found that the lactase persistence genotype, a proxy of long-term milk and total dairy intake was associated with a 44% increased risk of all-cause mortality in the intervention group advised to consume a Mediterranean diet rich in healthful plant foods, but with no difference in the control group that received contemporary low-fat dietary advice that placed a lesser emphasis on consumption of these foods.²⁰ Thus, the benefit found for the participants carrying the lactase non-persistence genotype in the Mediterranean diet group may have resulted from the substitution of dairy with healthful plant foods that they were instructed to consume. Indeed, such a hypothesis is supported by the findings from this same population that a high intake of fruit, nuts, dietary fiber, and polyphenols were each observationally associated with between a 37% and 63% decreased risk of all-cause mortality.²¹ ²² ²³

Interestingly, despite being susceptible to the problem of dietary substitution with unhealthful foods, a positive, albeit non-significant association between the lactase persistence genotype and risk of all-cause mortality has also been observed in multiple other MR studies.²⁴ ²⁵ ²⁶ For this review, a meta-analysis was carried out to examine this effect. Based on data from 4 MR studies involving 119,787 participants and 17,235 deaths, compared to other typically consumed foods, total dairy intake genetically predicted by the lactase persistence genotype was causally associated with an 8% increased risk of all-cause mortality (Figure 1). Importantly, an increased risk was evident across multiple genetic variants, suggesting this effect may be primarily explained by higher dairy intake as opposed to confounding by pleiotropy. Moreover, all 4 studies were carried out in the European Union where bovine growth hormone has been banned since 1990.²⁰ ²⁴ ²⁵ ²⁶ ²⁷ Thus, the causal association between total dairy intake and an increased risk of all-cause mortality is independent of artificial growth hormone use and in addition to the adverse effects caused by lactose intolerance. It is also important to recognize that these estimates reflect only about a 1% increment in energy intake given the findings that the lactase persistence genotypes are associated with between 20 to 40 g/day increase in dairy intake, primarily from fluid milk.¹⁴ ¹⁵ ²⁰

Figure 1. Effect of a 1% increment in energy from total dairy genetically predicted by the lactase persistence genotypes and relative risk of all-cause mortality in a meta-analysis of 4 Mendelian randomization studies involving 119,787 participants and 17,235 deaths. Genotypes include lactase non-persistence (CC), lactase persistence heterozygous (CT), and lactase persistence homozygous (TT).

The adverse effect of dairy foods on mortality may be partly explained by differences in macronutrient quality. Some, but not all studies found that substituting plant protein with dairy protein was associated with an increased risk of all-cause mortality.²⁸ ²⁹ ³⁰ For this review, a meta-analysis was carried out to examine this effect. Based on data involving 618,142 participants with 10.8 million person-years of follow-up from 4 prospective cohort studies, substituting 6% of energy (the equivalent energy from protein in a protein shake in a 2,000 kcal diet) from plant protein with dairy protein was associated with an 18% increased risk of all-cause mortality (Figure 2).

Dairy is also a major source of saturated fat that likely contributes to an increased risk of premature death. A recent prospective cohort study with 8.1 million person-years of follow-up found that substituting 5% of energy from total plant fat and fat from grains with dairy fat was associated with a 9% and 20% increased risk of all-cause mortality, respectively.³¹ A meta-analyses of 3 prospective cohort studies found that substituting each 5 g/day serving of olive oil with butter was associated with a 6% increased risk of all-cause mortality.³ A recent pooled analysis of 3 Harvard prospective cohort studies with up to 33 years of follow-up found that substituting each 10 g/day serving of plant oils with butter was associated with a 21% increased risk of all-cause mortality.³² Consistent with these findings, a meta-analysis of 8 prospective cohort studies commissioned by the World Health Organization found that substituting 5% of energy from carbohydrate, monounsaturated fat, or polyunsaturated fat with saturated fat was associated with between a 9% and 19% increased risk of all-cause mortality.³³ Moreover, a recent study with up to 45 years of follow-up found that substituting 5% of energy from monounsaturated fat and carbohydrate with saturated fat, of which dairy was the top source of, was associated with a 31% and 18% increased risk of all-cause mortality, respectively.³⁴

Some, but not all studies found that animal-derived monounsaturated fat, which dairy fat is a major source of, was associated with an increased risk of all-cause mortality.³⁵ ³⁶ ³⁷ ³⁸ For this review, a meta-analysis was carried out to examine this effect. Based on data involving 730,635 participants with 11.1 million person-years of follow-up from 5 prospective cohort studies, substituting up to 5% of energy from carbohydrate of non-specific quality with animal-derived monounsaturated fat was associated with a 12% increased risk of all-cause mortality (Figure 3). In addition, substituting 5% of energy from plant-derived monounsaturated fat with either animal-derived monounsaturated fat, saturated fat, or a combination of animal-derived monounsaturated fat and saturated fat was associated with between a 17% and 31% increased risk of all-cause mortality.

Figure 2. Effect of substituting 6% of energy from plant protein with dairy protein and relative risk of all-cause mortality in a meta-analysis of 5 prospective cohort studies involving 618,142 participants with 10.8 million person-years of follow-up.

Figure 3. Effect of substituting up to 5% of energy from animal and plant-derived monounsaturated fat with other major sources of energy and relative risk of all-cause mortality in a meta-analysis of 5 prospective cohort studies involving 730,635 participants with 11.1 million person-years of follow-up.

A Cochrane review of randomized controlled trials found that saturated fat reduction significantly reduced cardiovascular events, but while numerically lower, was not found to significantly reduce the risk of all-cause mortality.³⁹ This is not surprising given that great enough adherence for a long enough duration of time in a large enough number of participants would likely be necessary to demonstrate a significant effect, which can be difficult to achieve in trials of lifestyle interventions where compliance is often poor. As such, non-significant findings for mortality have also been reported in clinical trials of smoking cessation.⁴⁰ Therefore, to help deal with the problems of noncompliance and study heterogeneity that may arise from differences in intake between studies, the data was reanalyzed here to determine the effect on mortality per change in total cholesterol using the adjusted odds ratio based on methods described elsewhere.⁴¹

In a meta-analysis of 10 randomized controlled trials involving 55,725 participants and 3,515 deaths, reducing dietary saturated fat non-significantly reduced the odds of all-cause mortality by 22% per 1 mmol/L (38.67 mg/dL) reduction in total cholesterol. However, in a leave-out-one sensitivity analysis that excluded the Sydney Diet-Heart trial, the main contributor to between-study heterogeneity which accounted for less than 2% of deaths, reducing dietary saturated fat significantly reduced the odds of all-cause mortality by 26% per 1 mmol/L reduction in total cholesterol for 5 years of cumulative exposure (Figure 4). It is important to recognize that in the Sydney Diet-Heart trial, saturated fat was substituted partly with industrial trans-fat, as opposed to carbohydrate and polyunsaturated fat used in most other studies.⁴² Controlled feeding experiments have established that substituting saturated fat with trans-fat reduces total cholesterol, mainly due to reductions in HDL, helping to explain the reduction in total cholesterol observed in this study.⁴³

A reduction in dietary cholesterol, which dairy foods are a source of, may explain up to 20% of the reduction in total cholesterol found in the saturated fat reduction trials, and therefore likely contributed to the reduction in all-cause mortality.⁴⁴ This evidence of harm is consistent with the findings from a meta-analysis of 14 prospective cohort studies that each 100 mg/day increment in dietary cholesterol intake was associated with a 6% increased risk of all-cause mortality, with similar estimates reported in a subsequent study.⁴⁵ ⁴⁶ Importantly, even if it is assumed that almost all of the reduction in total cholesterol observed in these dietary trials was from LDL, this would still indicate an at least two-fold greater reduction in all-cause mortality per unit lower LDL than observed in statin trials with a similar median follow-up.⁴⁷

Figure 4. Effect of reducing dietary saturated fat and odds of all-cause mortality per 1 mmol/L reduction in total cholesterol in a meta-analysis of 10 randomized controlled trials involving 55,725 participants and 3,515 deaths. Subgroup 1.1.2 RR=0.81 CI, 0.65-1.00 (data not shown). Difference in all-cause mortality and change in absolute total cholesterol were derived from Analysis 1.1 and Analysis 3.1, respectively, from Hooper 2020.

The adverse effect of dairy foods on mortality may also be partly explained by differences in micronutrient composition, including a high content of calcium. A MR study found that lifelong exposure to higher circulating calcium was causally associated with 28% lower odds of longevity per 0.09–0.12 mmol/L increment in circulating calcium, a change comparable to that found for supplementation of 1,000 mg/day calcium.⁴⁸ An analysis of 2 prospective cohort studies involving 398,647 participants with 4.8 million person-years of follow-up found that compared to participants with median levels of circulating calcium, participants with the highest levels had a 10% increased risk of all-cause mortality.⁴⁹ However, a meta-analysis of randomized controlled trials found a non-significant increase in risk of all-cause mortality for calcium supplementation.⁵⁰ The failure to find a significant effect in clinical trials may be explained by poor adherence due to the discontinuation of calcium supplementation in participants experiencing adverse gastrointestinal effects, a low number of cases, and a short duration of exposure.¹⁹

Dairy foods are deficient in dietary fiber and generally have a lower average antioxidant content than healthful plant foods.⁵¹ Evidence from over 100 prospective cohort studies has found that even modest increments in intake of dietary fiber and plant-derived antioxidants, which are surrogate markers of healthful plant food intake were associated with between a 6% and 28% decreased risk of all-cause mortality.⁵² ⁵³ ⁵⁴ ⁵⁵ ⁵⁶ ⁵⁷ ⁵⁸ ⁵⁹ These findings were more pronounced in studies examining circulating biomarkers of dietary intake which may help mitigate measurement error associated with dietary questionnaires commonly used in epidemiological studies (Table 1). There are more than 25,000 known bioactive food constituents, of which the vast majority are antioxidants derived from plants. Given the established benefits of the oxidative stress-reducing and arterial blood flow-promoting properties of many antioxidants it is reasonable to expect that many of these less well-studied antioxidants found almost exclusively in minimally processed plant foods may have combined additive or synergistic effects on reducing multiple major causes of death, explaining evidence of a benefit of substituting dairy with healthful plant foods.⁵¹

Table 1. Meta-analyses of plant-derived nutrients measured as dietary or circulating concentration and relative risk reduction of all-cause mortality.

There are likely multiple underlying mechanisms by which the substitution of healthful plant foods with dairy foods increases the risk of premature death. These include Apolipoprotein B (ApoB), blood pressure, flow-mediated dilation, inflammation, body fat, and insulin-like growth factor-1. Evidence from over 100 randomized controlled trials and Mendelian randomization studies involving 2 million participants has unequivocally established that lowering LDL and ApoB reduces the risk of all-cause mortality, and that ApoB which represents the total number of circulating atherogenic lipoprotein particles is the primary lipid determinant of this.⁶⁰ ⁶¹ ⁶² ⁶³ ⁶⁴ Importantly, a recent MR study involving 347,797 participants found that there was no evidence of a threshold at which a further decrease in ApoB and LDL does not confer greater benefit on mortality reduction.⁶⁵ Specifically, evidence from randomized controlled trials indicate that each 10 mg/dL reduction in ApoB reduces all-cause mortality by 8% for 4.7 years of cumulative exposure.⁶⁰

Evidence from over 1,000 controlled dietary experiments has also unequivocally established that plant-based diets and the associated nutrients reduce atherogenic blood lipids.⁶⁶ ⁶⁷ ⁶⁸ ⁶⁹ ⁷⁰ ⁷¹ ⁷² ⁷³ ⁷⁴ ⁷⁵ ⁷⁶ ⁷⁷ Specifically, the substitution of dairy and other animal protein with plant protein,⁷⁸ reducing the intake of dietary cholesterol,⁷⁹ ⁸⁰ and increasing the intake of soluble fiber⁸¹ and plant sterols⁸² each reduce ApoB by up to 5 to 10 mg/dL. Importantly, based on evidence from 104 controlled feeding experiments,⁸³ substituting equal parts of energy from carbohydrate, monounsaturated fat, and polyunsaturated fat with 5% of energy from saturated fat would increase ApoB by 37 mg/dL, predicting a 36% increased risk of all-cause mortality for 4.7 years of cumulative exposure.

A meta-analysis of 57 randomized controlled trials found that reducing systolic blood pressure significantly reduces the risk of all-cause mortality, a finding that has been corroborated by MR studies.⁸⁴ ⁸⁵ Specifically, evidence from randomized controlled trials indicate that each 10 mmHg reduction in systolic blood pressure reduces the risk of all-cause mortality by 13% for 3.8 years of cumulative exposure. The benefits of substituting dairy with healthful plant foods are in part supported by the evidence from over 190 randomized controlled trials establishing that soluble fiber and plant-derived antioxidants reduce blood pressure.⁸⁶ ⁸⁷ ⁸⁸ ⁸⁹ ⁹⁰ ⁹¹ Importantly, a recent meta-analysis of 5 randomized controlled trials found that substituting 2 cups per day of ultra-processed or unsweetened soy milk with low fat dairy milk increases systolic blood pressure (SBP) by 8.00 mmHg and diastolic blood pressure (DBP) by 4.74 mmHg.⁹² The increase in SBP alone would predict a 12% increased risk of all-cause mortality for 3.8 years of cumulative exposure.

Flow-mediated dilation (FMD), which measures the dilation of an artery in response to increased blood flow is considered a gold standard for measuring vascular endothelial function, with each 1% reduction in FMD observationally associated with an 11% increased risk of all-cause mortality.⁹³ A meta-analysis of 90 controlled dietary experiments, for which more than half included dairy fat, found that a single high fat meal reduced postprandial FMD, and that meals with greater than 80% fat reduced FMD by 2.77% after 3 hours.⁹⁴ A randomized, crossover, controlled feeding trial found that substituting the equivalent energy from a combination of refined and unrefined sources of carbohydrate, monounsaturated fat, or polyunsaturated fat with 50 g/day butter reduced fasting FMD by 5.41% after 3 weeks.⁹⁵ This is an effect that would predict a 77% increased risk of all-cause mortality. In contrast, evidence from over 50 randomized controlled trials found that plant-derived antioxidants improve FMD.⁹⁶ ⁹⁷ ⁹⁸

Inflammatory biomarkers Interleukin 6 (IL-6) and C-reactive protein (CRP), whose synthesis is stimulated by IL-6 likely also play a role in longevity. IL-6 has been observationally and causally associated with an increased risk of all-cause mortality.⁹⁹ ¹⁰⁰ A recent meta-analysis of 5 randomized controlled trials found that substituting low fat dairy milk with ultra processed or unsweetened soy milk reduces CRP.⁹² A separate meta-analysis of randomized controlled trials found that based on 5 high quality studies, substituting dairy milk or protein with soy milk or protein reduces IL-6.¹⁰¹ The benefits of substituting dairy foods with healthful plant foods is corroborated by evidence from a further 120 randomized controlled trials establishing that dietary fiber and plant-derived antioxidants reduce CRP and IL-6.¹⁰² ¹⁰³ ¹⁰⁴ ¹⁰⁵ ¹⁰⁶ ¹⁰⁷ ¹⁰⁸

MR studies have found a causal association with a higher BMI and fat mass and an increased risk of all-cause mortality.¹⁰⁹ ¹¹⁰ MR studies have also found that compared to other typically consumed foods, genetically predicted total dairy intake is causally associated with an increased risk of obesity in both adults and adolescence, and in both developed and developing nations.¹¹¹ ¹¹² ¹¹³ ¹¹⁴ These findings were corroborated by a meta-analysis of ad libitum intervention trials lasting at least one year.¹¹⁵ The benefits of substituting dairy foods specifically with healthful plant foods is supported by a meta-analysis of 10 randomized, placebo-controlled trials without energy-restriction protocols that found that soluble fiber meaningfully reduces BMI, body weight, and body fat percentage.¹¹⁶

A meta-analysis of prospective cohort studies involving 30,876 participants indicated a U-shaped curve between Insulin-like growth factor-1 (IGF-1) and all-cause mortality mainly due to a greater risk of cancer mortality at high levels and a higher risk of cardiovascular mortality at low levels.¹¹⁷ However, a more recent study involving 394,082 participants found that high levels of IGF-1 were also associated with an increased risk of cardiovascular death.¹¹⁸ Moreover, IGF-1 was found to increase the risk of coronary heart disease and type II diabetes in a MR study, confirming a causal effect for elevated levels.¹¹⁹ MR studies have also confirmed the findings from epidemiological studies of an association between IGF-1 and an increased risk of Parkinson’s disease and colorectal, breast, and prostate cancers.¹²⁰ ¹²¹ ¹²² ¹²³ A meta-analysis of 8 randomized controlled trials found that dairy milk increases IGF-1 compared to other typically consumed foods.¹²⁴ Furthermore, a meta-analysis of 13 randomized controlled trials found that whey importantly contributes to this increase.¹²⁵

Dairy foods are commonly recommended to reduce the risk of fracture, however a meta-analysis of prospective cohort studies indicated no likely benefit independent of Vitamin D fortification.¹²⁶ In addition, two meta-analyses of MR studies found no benefit of dairy milk or dairy calcium intake on fracture risk compared to other typically consumed foods.¹²⁷ ¹²⁸ Dairy is also rich in nutrients that may adversely affect bone health. A meta-analysis of epidemiological studies found that a high intake of saturated fat and animal-derived monounsaturated fat was associated with a 79% increased risk of hip fracture and a 129% increased risk of overall bone fractures, respectively.¹²⁹ These observations are corroborated by the findings from MR studies that LDL and circulating arachidonic acid, a fatty acid found in dairy and other animal foods are causally associated with lower bone mass density, and that arachidonic acid is also causally associated with an increased fracture risk.¹³⁰ ¹³¹ ¹³² Moreover, a meta-analysis of epidemiological studies found that foods naturally rich in Vitamin C were associated with a 34% decreased risk of fracture rate and osteoporosis, suggesting a possible benefit of substituting dairy, particularly high fat dairy with fruits and vegetables.¹³³

Epidemiological studies have also found that substituting healthful plant foods with dairy is associated with an increased risk of multiple major causes of death. A meta-analysis of 5 prospective cohort studies found that substituting sources of plant protein, including nuts and legumes with dairy was associated with an increased risk of cardiovascular disease, corroborating the findings from primate models of experimental atherosclerosis that casein and whey accelerates the progression of atherosclerotic plaque volume by up to 10-fold compared to soy protein.² ¹³⁴ ¹³⁵ ¹³⁶ ¹³⁷ ¹³⁸ A pooled analysis of 3 cohorts found that substituting whole grains with dairy was associated with an increased risk of total cancer mortality.¹⁷ The Nurses’ Health Study found that substituting nuts, legumes, and whole grains with milk, cheese, and yogurt was associated with an increased risk of frailty, with a 47% increased risk found for the substitution of 5% of energy from plant protein with dairy protein.¹³⁹ ¹⁴⁰ The Adventist Health Study-2 found that substituting median intakes of soy milk with dairy milk was associated with a 67% increased risk of breast cancer, with no evidence of a threshold in which a further decrease in dairy milk did not confer greater benefit down to zero intake.¹⁴¹

Dairy has also been associated with an increased risk of major causes of death even when compared to non-specific, typically unhealthy foods. Meta-analyses of prospective cohort studies have found an association between total dairy intake and prostate cancer and lactose intake and ovarian cancer.¹⁴² ¹⁴³ In addition, dairy milk was associated with an increased risk of Parkinson’s disease in a meta-analysis of prospective cohort studies and in most subsequent cohort studies.¹⁴⁴ ¹⁴⁵ ¹⁴⁶ ¹⁴⁷ ¹⁴⁸

Multiple MR studies have confirmed a causal association between dairy foods and Parkinson’s disease, including a recent study which found that mozzarella cheese causes a 10-fold increase in risk.¹⁴⁹ ¹⁵⁰ ¹⁵¹ For this review, a meta-analysis was carried out to examine the effect for a one serving per day increment in dairy intake genetically predicted by the lactase persistence genotype. When estimates were reported per additional dairy consuming allele, it was assumed to represent a 20 g/day increment in total dairy intake and was rescaled to a 200 g/day increment in intake. Based on data from 3 MR studies involving 435,707 participants and 28,560 cases of Parkinson’s disease, compared to other typically consumed foods, each single serving per day increment in total dairy intake was causally associated with a 107% increased risk of Parkinson’s disease (Figure 5).

Figure 5. Effect of a one serving per day increment in genetically predicted total dairy intake and relative risk of Parkinson’s disease in a meta-analysis of 3 Mendelian randomization studies involving 435,707 participants and 28,560 cases of Parkinson’s disease.

In addition to the burden likely caused by chronic and degenerative diseases, dairy foods also have a deleterious effect on the quality of life brought about by lactose intolerance, prevalent in about 70% of the global population.¹⁵² Dairy food production also has an indirect adverse effect on health due to environmental impact. Compared to soy milk, dairy milk production generates 3-fold more greenhouse gas emissions, and requires 14-fold increase in land and 23-fold increase in fresh water use.¹⁵³

The role of dairy foods in the development of cardiovascular disease and cancer has been suspected for well over a century.¹⁵⁴ ¹⁵⁵ ¹⁵⁶ The evidence eventually led to policy changes by numerous governments to reduce dairy fat which was followed by substantial reductions in cardiovascular death and increases in life expectancy.¹⁵⁷ ¹⁵⁸ This was particularly evident in Finland. By the 1960s, the Finnish population which subsisted on diets rich in dairy fat had the highest rate of cardiovascular mortality in the world and a low life expectancy relative to other developed European nations. This prompted the launch of the North Karelia Project in eastern Finland, which was later extended nationally and included a key aim of improving the quality of dietary fat, particularly through a reduction in dairy fat and an increase in fruit and vegetable intake.¹⁵⁹ ¹⁶⁰ Life expectancy subsequently increased by 11.6 years in men and 9.2 years in women, with half of this increase explained by a reduction in cardiovascular mortality, and despite a doubling in smoking prevalence among women over the same period.¹⁶¹¹⁶² Similar findings were observed in the former communist nations of Eastern Europe following the abolishment of subsidies on dairy and other animal fats with the breakup of the Soviet Union.¹⁶³ ¹⁶⁴ ¹⁶⁵ ¹⁶⁶

Consistent with these observations, the 50-year follow-up of the Seven Countries Study found that high-fat milk and total animal foods were associated with an increased risk, and total plant foods with a decreased risk of coronary heart disease mortality.¹⁶⁷ In addition, saturated fat was associated with an increased risk and total plant foods with a decreased risk of all-cause mortality.¹⁶⁸ Moreover, a recent analysis of food supply data for 101 countries from 1961-2018 found that a higher ratio of plant protein to animal protein and lower fat supplies were associated with greater overall life expectancy.¹⁶⁹

In the 1920s, John Boyd Orr, a spokesperson for British Milk Marketing brought the Maasai, a nomadic group that inhabit Kenya and Tanzania, to attention by associating a diet rich in meat and milk to apparent good health. Orr, however, failed to recognize that historically, many Maasai communities were forced to fall back to plant-based diets during the frequent periods of significant livestock loss, and the inevitable influence this would have had on future health.¹⁷⁰ Nevertheless, Orr conceded that 80% of the Maasai reported rheumatoid arthritis and habitual constipation.¹⁷⁰ History repeated itself when research supported in part by the livestock industry revisited the Maasai in the 1960s and failed to sufficiently recognize the nutritional impact of the near-famine state sustained for 4-6 months during the dry season each year, let alone the severe drought and flooding in the Maasailand in the prior decade that resulted in the loss of up to 80% of livestock.¹⁷¹ ¹⁷² Interestingly, an autopsy study of 50 confirmed Maasai funded by the meat industry men found that the extent of atherosclerosis was at least comparable to that observed in U.S. men.¹⁷³

Health issues were perhaps even more apparent in the nomadic pastoralist populations of Central Asia less susceptible to such severe livestock loss and frequent famines. In the 1960s the prevalence of coronary heart disease among the nomadic pastoralists of Xinjiang described as subsisting chiefly on sources of animal fat was up to more than 30 times higher than populations in other parts of China where saturated animal fat was scarcely consumed.¹⁷⁴ A century ago, Maxime Hans Kuczynski examined a population of nomadic pastoralists from the Eurasian Steppe, and attributed a “pure meat-milk-diet” to a high prevalence of obesity, stroke, premature extensive atherosclerosis, peripheral artery disease, kidney disease, gout, habitual constipation, and erectile dysfunction.¹⁷⁵ ¹⁷⁶ Kuczynski did not observe such health issues in their neighboring counterparts who consumed predominantly plant-based diets and retained sexual function into their seventies. These findings mirror the classical observations of Hippocrates who in 400 B.C.E described the nomadic Scythian as subsisting chiefly on grass-fed meat, raw milk, and cheese and having high rates of obesity, rheumatoid arthritis, gout, and erectile dysfunction.¹⁷⁷

While efforts have been made to reduce dairy fat, many health organizations still recommend up to 3 servings of reduced fat dairy per day despite mounting evidence of an increased risk of premature death compared to healthful plant foods and a lack of benefit on fracture risk. The overwhelming evidence from clinical, genetic, and epidemiological studies strongly indicate that each one serving per day substitution of healthful plant foods with reduced fat, full fat, or fermented dairy foods may increase the risk of all-cause mortality by a magnitude at least comparable to the 18% to 22% increased risk observed in meta-analyses for passive smoking, smokeless tobacco use, and high volume alcohol drinking. The evidence warrants a reexamination of the recommendations to consume dairy in any form and at any level of intake.

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Healthy Longevity

Dairy foods are a probable cause of premature death