Evidence is building that dairy foods may help reduce the risk of type 2 diabetes. Protective associations have been reported for total dairy consumption as well as for both low-fat and regular-fat dairy, and are particularly pronounced for fermented products such as yogurt and cheese.
Several components of dairy foods could potentially be involved in the reduced risk including protein, calcium, magnesium and dairy fatty acids, along with mechanisms related to fermentation. These are not mutually exclusive and may well interact in the dairy matrix to produce the beneficial effects. Since the number of people with type 2 diabetes is rising in European populations, even a small protective effect of dairy as part of a healthy diet could have important public health implications.
A number of epidemiological studies have reported that intake of milk and dairy food is associated with a reduced risk of developing type 2 diabetes. An overview of four prospective cohort studies in 2007 showed a reduction of about 15% in the risk of diabetes in the highest dairy consumers (3 to 5 compared with less than 1.5 servings/day)1. Similar reductions were reported in overviews in 2010 and 2011 based on five and seven cohorts respectively2,3. In the latter meta-analysis, the protective effect of dairy was largely attributable to low-fat dairy foods, and a further dose-response analysis (involving three of the studies) suggested a 10% reduction in type 2 diabetes for every additional serving of low-fat
Since these overviews, several more prospective studies looking at the relationship between dairy consumption and type 2 diabetes have been published, including for European populations. The EPIC-InterAct Study (an investigation in eight European countries to identify the genes and lifestyle factors that influence risk of type 2 diabetes)4 found that both cheese consumption and fermented dairy product intake (cheese, yogurt, and thick fermented milk combined) were associated with a reduced risk of diabetes. Similarly, in another EPIC cohort, this time in the UK and using 7-day food diaries, low-fat fermented dairy intake, largely driven by yogurt, was associated with a decreased risk of type 2 diabetes: 24% less between the highest and lowest consumers5. The PREDIMED study in an elderly Mediterranean population at high cardiovascular risk also reports that a healthy dietary pattern incorporating dairy products and, again, particularly yogurt, was protective against type 2 diabetes6. In the French DESIR cohort (Data from the Epidemiological Study on the Insulin Resistance Syndrome), those who consumed more than three servings of milk or yogurt a day had a lower risk of type 2 diabetes compared with those who consumed less than one serving a day7. Two other recent studies, in Danish and British cohorts, found no relationship between dairy intake and diabetes8,9. The Danish data did suggest a beneficial effect of cheese and fermented dairy on glucose regulation measures but these did not translate into a significant association with type 2 diabetes8. Another Danish study looking specifically at milk intake found no relationship with diabetes risk10. In the Dutch Maastricht Study, a high intake of full-fat products was positively related to diabetes risk11. However, individuals with a high total dairy consumption had lower risk of type 2 diabetes, and those with a high consumption of skimmed and fermented products had lower risk of impaired glucose metabolism11.
A systematic review and dose-response meta-analyses published in 2013 utilised the available data to investigate in more detail the relation between the intake of individual dairy foods and diabetes risk, as well as between regular- and low-fat dairy12. Seventeen cohort studies were included in the overall meta-analysis and a significant reduction in the risk of type 2 diabetes was reported with increasing intakes of total dairy products and low-fat dairy products (up to 300g - 400g per day) and with increasing intake of cheese (up to around 50g per day). Another meta-analysis published in 2013 also found that total dairy product consumption, low-fat dairy products and cheese were associated with a reduced risk of diabetes, and additionally in this overview, so was yogurt13. In this case, total dairy and low-fat dairy intake were associated with 6% and 12% respectively, lower risk of type 2 diabetes per 200g a day consumption, with most of the risk reduction occurring with intakes up to about 200g per day for total dairy, and 300g per day for low-fat dairy.
A more recent analysis of cohort studies to inform the 2015 Dutch Dietary Guidelines concluded that there is convincing evidence that yogurt consumption is associated with a lower risk of type 2 diabetes; yogurt intake of more than 60g a day was associated with a 15% reduction in diabetes risk, compared with intakes less than 10g per day14. Similarly, a meta-analysis in 2016 which summarised the evidence from 22 prospective cohort studies found yogurt consumption was associated with a reduced risk of type 2 diabetes at 80g/day, but not with higher intakes15. In this analysis, total dairy food consumption was also associated with a lower risk, mainly attributable to low-fat dairy foods; there were no associations with either milk or cheese intake. The same conclusion was reached from a systematic review published in 2016; namely, that there is high-quality evidence to support favourable associations between yogurt and low-fat dairy intake and reduced risk of type 2 diabetes16.
Randomised control trials are needed to further confirm the results of the cohort studies. One such recent small scale trial found that consumption of four servings of low-fat milk and yogurt a day for six months improved plasma insulin and insulin resistance without negatively impacting on body weight or blood lipids17. Similarly, a six-week trial of three servings of low-fat dairy a day resulted in improvements in fasting glucose in men18.
Several components of the dairy matrix could potentially be involved in the protective relationship between dairy and type 2 diabetes. These are not mutually exclusive and a combination of mechanisms may well produce beneficial effects on glycaemic control and other risk factors. These include dairy minerals such as calcium and magnesium: both have a role in regulating insulin-mediated intracellular processes1,19,20. Protein in dairy has also been shown to have beneficial effects on insulin secretion and blood glucose control21-24. The bioactive peptides that may be involved result from digestion of milk protein in the gut and from the fermentation process in foods such as cheese, yogurt and fermented milk. Similarly, a form of vitamin K (vitamin K2; part of the menaquinone family) which is associated with fermented dairy foods has been linked to reduced risk of type 2 diabetes25.
In addition, dairy fatty acids may play a role. Certainly, evidence from cohort studies suggests that the positive effect of dairy on diabetes risk is not restricted to low-fat dairy foods but also includes higher fat ones such as cheese. Data from the Malmö Diet and Cancer cohort, for example, indicated a decreased risk of type 2 diabetes with high intakes of regular-fat dairy foods but not with low-fat dairy26. A number of recent studies have found that the dairy-derived fatty acid trans-palmitoleate is associated with a substantially lower incidence of diabetes (60% less in one study)27-29. Other fatty acids in dairy have also been associated with reduce diabetes risk including odd-chain saturated fatty acids pentadecanoic acid (C15:0) and heptadecanoic acid (C17:0) and short-chain fatty acids (SCFA) including buyrate (C4:0); the branched-chain dairy fatty acid phytanic acid has been reported to have anti-diabetic effects including increasing insulin sensitivity30-32.
Dairy may also indirectly modify diabetes risk through beneficial effects on weight, body fat and central adiposity, and on muscle mass and function.
Additional research will help to differentiate the effects of individual dairy foods and components of the dairy matrix for diabetes risk particularly the relevance of fermented dairy products such as yogurt. Randomised control trials to confirm the results of cohort studies would also be useful. However, the protective effect of dairy suggested by evidence to date, has important public health implications given that there are already around 60 million people with diabetes in the European Region, and these numbers are increasing33.
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