What is the relationship between the intake of milk and milk products and metabolic syndrome?

Limited evidence is available showing intake of milk and milk products are associated with reduced risk of metabolic syndrome.

Intake of milk and milk products is associated with reduced risk of metabolic syndrome and may even be protective in certain population groups. The conclusion reached for this question is based on one systematic review with meta-analysis (Elwood, 2008), one prospective cohort study (Snijder, 2008) and two cross-sectional studies (Beydoun, 2008; Ruidavets, 2007).

Elwood et al, (2008) performed a systematic review and meta-analysis and the data showed a reduction in risk associated with the highest level of milk consumption for metabolic syndrome (RR=0.74; 95% CI: 0.64, 0.84) compared to the risk in those with low consumption.

Snijder et al, (2008) conducted a prospective cohort study investigating the association between dairy consumption and changes in weight and metabolic disturbances. The authors concluded that dairy consumption was not associated with changes in metabolic variables in a Dutch elderly population. Two cross-sectional studies (Beydoun, 2008; Ruidavets, 2007) looked at milk and milk product consumption and metabolic syndrome. The French study by Ruidavets et al, (2007) determined that the intake of dairy products was associated with a lower probability of insulin resistance syndrome. No significant (NS) associations between whole milk (per 100g), low-fat milk (per 100g) or skim milk (per 100g) and metabolic syndrome were observed in a study of National Health and Nutrition Examination Surveys (NHANES) 1999-2004 data (Beydoun, 2008).

Systematic Review/Meta-Analysis

Elwood et al, 2008 (positive quality) performed a systematic review and meta-analysis to investigate the literature on milk and dairy consumption and risk of vascular disease and diabetes, examine the evidence related to consumption of whole vs. reduced fat milk and disease risk and consider the likely effect of milk and dairy consumption on survival. The authors also reviewed a 2007 report by the World Cancer Research Fund to determine the impact of milk and dairy consumption on cancer risk. Using Cochrane systematic review methods, MEDLINE was searched up to June 2008 using key words milk/milk protein/dairy/dairy calcium and heart disease/coronary artery disease (CAD)/myocardial infarction (MI)/ischaemic heart disease (IHD), stroke and diabetes/metabolic syndrome. This search revealed 180 papers on milk and heart disease, 33 papers on milk and stroke, and 111 papers on milk and diabetes. Only studies that were done in human adults using population-based and prospective designs and reported baseline data on milk or dairy consumption, vascular disease outcome or incident diabetes were included in the final review. The final sample included 15 prospective studies on IHD and stroke, four prospective studies on diabetes, four case-control studies on metabolic syndrome and four case-control studies on MI. The data showed a reduction in risk associated with the highest level of milk consumption for metabolic syndrome (RR=0.74; 95% CI: 0.64, 0.84).

Prospective Cohort Study

Snijder et al, 2008 (positive quality), a prospective cohort study conducted in the Netherlands, investigated the association between dairy consumption and changes in weight and metabolic disturbances, based on data from the Hoorn study, a population-based cohort of white men and women aged 50-75 years. Average food intake was measured at baseline using a 92-item semi-quantitative food-frequency questionnaire (FFQ). At baseline and follow-up, participants underwent an extensive physical examination and a blood sample was drawn for biochemical analyses of fasting glucose, post-load glucose, high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) and triglycerides (TG). During the physical examination, weight, waist circumference (WC) and blood pressure (BP) were measured. 1,124 participants were included in the analysis. Baseline dairy consumption was not associated with changes in fasting and post-load glucose concentrations, serum lipid levels or BP, nor with the risk of developing metabolic syndrome in 6.4 years (OR=0.86, 95% CI: 0.52, 1.42, comparing highest with lowest quartile of dairy consumption). The authors concluded that dairy consumption was not associated with changes in metabolic variables in a Dutch elderly population.

Cross-Sectional Studies

Beydoun et al, 2008 (positive quality), a cross-sectional analysis of merged NHANES data from 1999-2004 in the US, assessed the association between consumption of dairy and related nutrients and obesity, central obesity and the metabolic syndrome. Out of 17,061 subjects over age 18 years (8,970 women and 8,091 men) with complete demographic data, 4,519 subjects had complete data on dietary intake (assessed from 24-hour recall data) and metabolic outcomes, such as weight, height, WC, BP and laboratory values (fasting blood glucose, triacylglycerol stores and HDL-C). On average, adults consumed 1.54 servings of dairy (0.90 in fluid milk and 0.60 in cheese) per day. Each serving of dairy products increased the risk of MetS by 8% among men. Odds ratios (OR) for one more daily serving of yogurt for metabolic syndrome was 0.40 (95% CI: 0.18, 0.89; P<0.05) and ORs for one more daily serving of cheese for metabolic syndrome was 1.16 (95% CI: 1.04, 1.29; P<0.05). No significant associations between whole milk (per 100g), low-fat milk (per 100g) or skim milk (per 100g) and metabolic syndrome were observed.

Ruidavets et al, 2007 (neutral quality), a cross-sectional study conducted in France, analyzed the relation between various food groups and the frequency of insulin resistance syndrome. Participants were recruited from the population as part of the French MONICA Study (Monitoring of Trends and Determinations in Cardiovascular Disease). Anthropometric data were taken, including WC, waist-to-hip ratio (WHR) and body mass index (BMI); BP was measured twice and fasting blood samples were analyzed for lipid and glucose measurements. Intakes of dairy products, fish or cereal grains were measured through food records with follow-up interviews by a dietitian. After those without complete data were excluded, 912 men aged 45-64 years remained in the analysis. The prevalence of insulin resistance syndrome was 23.5%, and it reached 29.0%, 28.1% and 28.1% when the intake was below the median for fish, dairy products and cereal grains, respectively. After adjustment for confounding variables, the ORs for insulin resistance syndrome (above median values vs. below) were 0.51 (95% CI: 0.36, 0.71) for fish, 0.67 (95% CI: 0.47, 0.94) for dairy products and 0.69 (95% CI: 0.47, 1.01) for cereal grains. When intakes of all three food groups were high, the odds ratio was 0.22 (95% CI: 0.10, 0.44), leading the authors to conclude that a high consumption of dairy products, fish or cereal grains is associated with a lower probability of insulin resistance syndrome, especially when intakes of all three food groups is high.