It has been estimated that 366 million people had diabetes (primarily type 2) in 2011, a number predicted to rise to 552 million by 2030 if current trends continue, note the authors, who set out to establish whether consuming dairy products can reduce the risk of developing it - and whether the type and amount of dairy is important.
Do different sources of dairy all confer the same benefits? And how much is enough?
Epidemiological studies have yielded mixed results, they observe, with some suggesting a decreased risk associated with higher intake of dairy products, but other studies finding no association.
Meanwhile, more detailed examinations of dose-response relationships between dairy intakes and type 2 diabetes needed to be conducted to establish whether there could be potential threshold effects, they add.
“In addition, it is important to establish whether the associations may differ according to the type of dairy product consumed and by study characteristics such as geographic location and adjustment for confounding factors.”
To find answers, they looked at the findings of 17 prospective cohort and nested case-control studies of dairy product intake and risk of type 2 diabetes up to June 5, 2013 (7 studies were from the US, 6 were from Europe, 2 were from Asia, and 2 were from Australia).
No significant association was observed for high-fat dairy products or total milk
They found that high intake of dairy products was associated with a significant decrease in the risk of type 2 diabetes.
“Significant inverse associations were also found for low-fat dairy products, low-fat or skim milk and cheese, and for yogurt in the high compared with low analysis, but no significant association was observed for high-fat dairy products or total milk.
“There was some evidence of an increased risk with intake of whole milk in the nonlinear analysis, which contrasted with the inverse associations with low-fat dairy products and with low-fat or skim milk. This suggests that the fat content of some dairy products might offset the beneficial effect of other nutrients in dairy foods.
“Any additional studies should assess the association between other specific types of dairy products and the risk of type 2 diabetes and adjust for more confounding factors.”
What is it about dairy that might be responsible for the beneficial effects?
But what is it about dairy that confers these apparently beneficial effects? Calcium? Vitamin D? Magnesium? Whey protein?
Animal and human studies show that calcium increases insulin secretion and is essential for insulin-responsive tissues such as skeletal muscle and adipose tissue and may reduce insulin resistance, note the authors. Meanwhile, some dairy products are fortified with vitamin D, which has been shown to be associated with reduced diabetes risk, possibly by influencing insulin secretion and reducing insulin resistance.
However, the Women’s Health Initiative randomized trial found no association between supplementation with calcium and vitamin D on incident type 2 diabetes, they point out.
Meanwhile, whey protein has been shown to help people manage their body weight and increase insulin sensitivity in animals, while magnesium has been associated with reduced diabetes risk in epidemiological studies, and with improved insulin sensitivity in some experimental studies.
National Dairy Council
Commenting independently on the study, which was not funded by the dairy industry, National Dairy Council Senior Vice President for Nutrition Research Jeffrey Zachwieja, PhD told FoodNavigator-USA that "while their findings suggest that no one dairy product drives the association, total dairy, low-fat milk and cheese consumption were significantly associated with a reduced risk of type II diabetes".
He added: "The Centers for Disease Control has sounded the alarm that diabetes is the next big health epidemic and this new report strengthens the growing data showing that dairy foods may be a part of the solution in reducing risk of type 2 diabetes.
"These are very positive, yet observational data and the strength of existing data on dairy consumption and reduced risk for type 2 diabetes provides a strong basis for federal research resources to be allocated toward clinical and community dairy intervention trials in at risk populations to reduce the occurrence of type 2 diabetes."
Study limitations
As to potential confounding factors, the authors acknowledge that higher intakes of low-fat dairy in particular may be associated with other healthy behaviors including higher levels of physical activity, higher intakes of fiber and whole grains, lower prevalence of smoking and overweight/obesity, and lower intakes of red and processed meat.
But they add: “Many of the studies included in this meta-analysis adjusted for known confounding factors such as age, BMI, smoking, and fiber and energy intake.”
Source: American Journal of Clinical Nutrition. August 14, 2013 doi: 10.3945/ajcn.113.059030.
‘Dairy products and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies’
Authors: Dagfinn Aune, Teresa Norat, Pa°l Romundstad, and Lars J Vatten