Regular consumption of milk is not associated with increased levels of cholesterol, according to an almost 2m-person Mendelian analysis, published in the International Journal of Obesity. The analysis also suggests that those who regularly consumed milk had a 14% lower risk of coronary heart disease.
Researchers from the University of Reading, University of South Australia, Southern Australian Health and Medical Research Institute, University College London, and University of Auckland worked together on the study.
The research was conducted following several contradictory studies that have previously investigated the causal link between higher dairy intake and cardiometabolic diseases such as obesity and diabetes, the authors note. To account for inconsistencies in sampling size, ethnicity and other factors, the team conducted a meta-analysis of data in up to 1.9 million people and used the genetic approach to avoid confounding.
The research analysed three large population studies and found that people who regularly drank high amounts of milk had lower levels of both good and bad cholesterol, although their BMI levels were higher than non-milk drinkers. Further analysis of other large studies also suggests that those who regularly consumed milk had a 14% lower risk of coronary heart disease.
The researchers took a genetic approach to milk consumption by looking at a variation in the lactase gene associated with digestion of milk sugars known as lactose. The study identified that having the genetic variation where people can digest lactose was a good way for identifying people who consumed higher levels of milk.
Prof Vimal Karani, Professor of Nutrigenetics and Nutrigenomics at the University of Reading said: “We found that among participants with a genetic variation that we associated with higher milk intake, they had higher BMI, body fat, but importantly had lower levels of good and bad cholesterol. We also found that those with the genetic variation had a significantly lower risk of coronary heart disease. All of this suggests that reducing the intake of milk might not be necessary for preventing cardiovascular diseases.”
Obesity, diabetes, and other conditions that affect metabolism also have ties to over-indulging in dairy products. Despite this, the UK Biobank data showed those with the lactase mutation were 11 percent less prone to type 2 diabetes. Karani adds there was no evidence higher milk intake increased the chances of diabetes or inflammation.
Karani said: “The study certainly shows that milk consumption is not a significant issue for cardiovascular disease risk even though there was a small rise in BMI and body fat among milk drinkers. What we do note in the study is that it remains unclear whether it is the fat content in dairy products that is contributing to the lower cholesterol levels or it is due to an unknown ‘milk factor’”.
Evidence for a causal association between milk intake and cardiometabolic disease outcomes using a two-sample Mendelian Randomization analysis in up to 1,904,220 individuals
Authors: Karani Santhanakrishnan Vimaleswaran, Ang Zhou, Alana Cavadino & Elina Hyppönen
Published in the International Journal of Obesity on 24 May 2021
High milk intake has been associated with cardio-metabolic risk. We conducted a Mendelian Randomization (MR) study to obtain evidence for the causal relationship between milk consumption and cardio-metabolic traits using the lactase persistence (LCT-13910 C > T, rs4988235) variant as an instrumental variable.
We tested the association of LCT genotype with milk consumption (for validation) and with cardio-metabolic traits (for a possible causal association) in a meta-analysis of the data from three large-scale population-based studies (1958 British Birth Cohort, Health and Retirement study, and UK Biobank) with up to 417,236 participants and using summary statistics from consortia meta-analyses on intermediate traits (N = 123,665–697,307) and extended to cover disease endpoints (N = 86,995–149,821).
In the UK Biobank, carriers of ‘T’ allele of LCT variant were more likely to consume milk (P = 7.02 × 10−14). In meta-analysis including UK Biobank, the 1958BC, the HRS, and consortia-based studies, under an additive model, ‘T’ allele was associated with higher body mass index (BMI) (Pmeta-analysis = 4.68 × 10−12) and lower total cholesterol (TC) (P = 2.40 × 10−36), low-density lipoprotein cholesterol (LDL-C) (P = 2.08 × 10−26) and high-density lipoprotein cholesterol (HDL-C) (P = 9.40 × 10−13). In consortia meta-analyses, ‘T’ allele was associated with a lower risk of coronary artery disease (OR:0.86, 95% CI:0.75–0.99) but not with type 2 diabetes (OR:1.06, 95% CI:0.97–1.16). Furthermore, the two-sample MR analysis showed a causal association between genetically instrumented milk intake and higher BMI (P = 3.60 × 10−5) and body fat (total body fat, leg fat, arm fat and trunk fat; P < 1.37 × 10−6) and lower LDL-C (P = 3.60 × 10−6), TC (P = 1.90 × 10−6) and HDL-C (P = 3.00 × 10−5).
Our large-scale MR study provides genetic evidence for the association of milk consumption with higher BMI but lower serum cholesterol levels. These data suggest no need to limit milk intakes with respect to cardiovascular disease risk, with the suggested benefits requiring confirmation in further studies.
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