Cow’s milk and dairy products derived from this complex food source have long been proposed as beneficial to human health, yet underlying clinical evidence supporting direct benefit to cardiometabolic health continues to raise controversy, based primarily on the high saturated fatty acid (SFA) content of whole-fat dairy. Whether high levels of dietary SFAs per se do indeed initiate a cascade of worsening intermediary blood markers including an adverse lipoprotein profile, and in turn lead to higher prevalence of cardiometabolic disease is now under considerable scrutiny. This narrative review aims to present the most recent evidence from both observational cohorts and randomized controlled trials (RCTs) that investigate the relationships between dairy and risk of cardiovascular disease (CVD) and type 2 diabetes (T2D), and to evaluate the evidence provided by these different study types. Also to identify, where possible, potential mechanisms by which dairy nutrients may promote health benefits.

Concern around dairy and potential adverse health outcomes arose from early epidemiologic data which supported a strong association between animal-origin food groups that provide a major source of dietary SFAs and an increased risk of CVD (1). In countries such as the UK, milk and dairy foods contribute almost 30% of SFA intake, and so quite reasonably have been considered a food component of concern (2). However, current literature shows growing support for the proposal that dairy products may have a neutral or even positive effect on CVD outcomes (3), with a number of meta-analyses supporting this relationship (4–9). There is also a new but growing consensus that the matrix of a whole-fat food such as dairy may be more important than the content and composition of component isolated fatty acids. Such that food-based rather than nutrient-based recommendations should be developed for CV health (3, 10, 11). It is notable however that the predominance of this evidence is obtained from observational studies. There is less evidence from RCTs, particularly with reference to incident CVD where long-term dairy interventions evaluating hard CV event points are lacking. This may be critical when aiming to interpret findings suggestive of a positive relationship with regular- and high-fat diary, and in order to develop robust public health recommendations.

A number of meta-analyses and systematic reviews have also focused on dairy and T2D (4, 12–17), again showing an inverse association between dairy intake and risk of T2D in observational studies. A recent expert panel position paper (18) reported a number of key findings including the evidence from large prospective cohort studies that total dairy consumption has a neutral or moderately beneficial effect on T2D risk. Again notably this is an outcome supported only by limited evidence from randomized controlled trials (RCTs) (19), with no long-term interventions investigating the effect of high-fat dairy on incident T2D. Dairy category is clearly important, again with evidence from prospective cohort studies showing fermented yogurt to be most strongly associated with lower T2D risk. There is with sparse evidence from RCTs. Even in 2020, the balance of evidence is predominantly from observational studies. Larger and longer duration clinical intervention trials are needed, with incident T2D as the primary outcome. RCTS are also required for better understanding of the underpinning mechanisms by which dairy may potentially be protective.

Dairy composes about 10% of the energy consumed in, for example, a typical North American diet, of which approximately half is from fluid milk, half from fermented (or “cultured”) cheese, and a small percentage from fermented yogurt (20). Important nutrients found in the myriad of dairy formats include milk proteins, calcium, magnesium, potassium, medium- and odd-chain saturated fats, specific fatty acids, and low-glycemic index (GI) sugars; shown to have beneficial effects on aspects of glucose control, insulin secretion, insulin sensitivity and/or T2D risk (21) as well as a range of CV risk factors (22). Notably a number of authors (23–26) have recently highlighted the importance of focusing on foods and dietary patterns rather than simply individual dietary nutrients when assessing CVD and T2D risk. In turn it is clear that expanding response to these dietary patterns beyond simple body fatness and circulating blood lipids into the multiple risk outcomes now identified as important to CV health is important.

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