Quick Quiz #1
When it comes to cardiovascular health, dairy products are:
The answer, according to a recently published systematic review (1) of the relationship between dairy product consumption and risk of cardiovascular-related clinical outcomes is “Beneficial” or “Neutral”. There is no evidence of a detrimental association.
This is interesting, as conventional wisdom has suggested that we need to avoid many dairy products, particularly the high-fat dairy products like cheese, in order to lower risk for cardiovascular-related clinical outcomes like high blood pressure, type 2 diabetes, stroke or coronary artery disease.
While this systematic review by Drouin-Chartier and his colleagues is by no means the final word on the subject, it sheds considerable light on what we know so far. There are definitely gaps in our knowledge, and more studies will be needed to further clarify the situation.
Let’s take a closer look at what we know so far. Jump ahead to read the details about hypertension, type 2 diabetes, stroke, metabolic syndrome, cardiovascular disease or coronary artery disease. Want the low-down on high-fat vs. low-fat dairy? Skip ahead to Quick Quiz #2.
High-quality evidence shows that total dairy product consumption lowers the risk of high blood pressure. The “high-quality” grade given to the evidence is due to the consistent direction and magnitude of the association.
In addition, moderate-quality evidence further reveals that low-fat dairy and milk are associated with decreased risk of hypertension.
There is no association between cheese consumption and risk for high blood pressure. That is, the effect of cheese is neutral based on high-quality evidence.
Similarly, there is no association between yogurt consumption and high blood pressure. In this case the neutral effect is based on moderate-quality evidence.
High-quality evidence shows that low-fat dairy consumption lowers risk of type 2 diabetes, while high-fat dairy has a neutral effect based on moderate-quality evidence.
In the case of yogurt, high-quality evidence also points to the association between eating yogurt and a reduced risk for type 2 diabetes.
Moderate-quality evidence shows that total dairy consumption and cheese consumption lowers risk of type 2 diabetes.
Finally, when it comes to milk, there appears to be no effect of milk on the risk for type 2 diabetes, based on moderate-quality evidence.
While the association between total dairy intake and reduced risk was judged to be “robust”, because the study populations of three of meta-analyses used in this systematic review were considered to be homogeneous, the authors of this systematic analysis downgraded the overall score from high-quality to moderate-quality evidence.
While both low-fat dairy and cheese are associated with a lower risk of stroke, it isn’t yet clear if lower-fat dairy is more beneficial than higher-fat dairy products. We don’t yet have the evidence to make a recommendation in this regard.
Moderate-quality evidence shows that both total dairy consumption and specifically milk consumption decrease risk of metabolic syndrome.
There is a lack of data to be able to assess cheese consumption, yogurt consumption and low-fat vs high-fat dairy consumption with regard to the risk for metabolic syndrome.
Metabolic syndrome is the presence of a cluster of risk factors that raise the risk for heart disease, diabetes or stroke. The risk factors comprising metabolic syndrome are: a large waistline, high levels of triglycerides, low levels of HDL (the “good” cholesterol), high blood pressure and a high fasting blood sugar level. The presence of three out of these five risk factors indicates metabolic syndrome.
Evidence supports either favorable or neutral associations between the consumption of total dairy and cardiovascular disease, resulting in a grade of moderate-quality evidence that total dairy consumption is neutral for cardiovascular disease risk.
There is high quality evidence that cheese intake is not associated with the risk of cardiovascular disease. That is to say, the effect is neutral.
When it comes to yogurt, moderate quality evidence shows the association between yogurt consumption and cardiovascular disease is neutral.
As far as low-fat vs high-fat dairy, there is simply a lack of meta-analyses to draw any conclusion.
Overall, we can say there is moderate- to high-quality evidence that total dairy intake, cheese intake and yogurt intake have a neutral effect on cardiovascular disease risk.
High quality evidence shows a neutral association between total dairy consumption and coronary artery disease risk. As well, again from high-quality evidence, there is a neutral association between dairy fat intake and coronary artery disease risk.
When it comes to milk, yogurt and cheese, again there is a neutral effect, this time from moderate-quality evidence in all three cases.
Is there sufficient evidence to recommend the consumption of low-fat as opposed to regular-fat dairy to reduce risk of cardiovascular-related clinical outcomes?
The answer, so far, is “No.” According to the authors of this review, “there is no evidence from this extensive review that the consumption of dairy fat or of regular- and high-fat dairy is detrimental to cardiovascular-related clinical outcomes.” Note that when the authors of this systematic review refer to dairy product consumption, they are excluding butter, as butter is not considered to be part of the dairy food group in most dietary guidelines.
In a companion review paper (2), Drouin-Chartier and his colleagues examined randomized controlled trials looking at the consumption of dairy products and cardiovascular risk factors. This review also came to a similar conclusion: Whether high-fat or low-fat, dairy product consumption is not associated with any increased risk for blood pressure, inflammation, insulin resistance, lipid levels or vascular function.
The bottom line
In short, the evidence shows dairy products, even high-fat dairy products, do no harm and may actually offer benefit for some cardiovascular risk factors and outcomes, calling prevailing recommendations into question. This suggests that if someone enjoys drinking 2% milk, perhaps we should hold back on advice to “switch to 1% or skim,” as evidence doesn’t support the need to do this for cardiovascular health.
How the systematic review was done
The researchers reviewed all the meta-analyses of prospective epidemiological studies that looked at dairy product consumption and cardiovascular clinical outcomes, including cardiovascular disease, coronary artery disease, stroke, hypertension, type 2 diabetes and presence of metabolic syndrome. A total of 21 studies were reviewed.
Prospective studies follow a population over a period of time and watch for the outcomes of interest. The advantage of this type of study is that it minimizes recall error.
In addition to total dairy consumption (excluding butter), when possible, the authors also looked at individual dairy products (e.g. milk, yogurt, cheese), high-fat vs regular-fat vs low-fat dairy consumption, and fermented vs non-fermented dairy products and how these had an effect on the various clinical outcomes.
Evidence was graded as high-quality, moderate-quality, low-quality or very low-quality, based on a system of scoring the evidence known as the GRADE scale, a widely recognized, systematic method of scoring evidence. High-quality evidence means “we are very confident that the true effect lies close to that of the estimate of the effect” in this system.
(1) Drouin-Chartier J-P et al. Systematic review of the association between dairy product consumption and risk of cardiovascular-related clinical outcomes. Adv Nutr 2016 (7); 1026-1040.
(2) Drouin-Chartier J-P et al. Comprehensive review of the impact of dairy foods and dairy fat on cardiometabolic risk. Adv Nutr 2016. (7); 1041-1051.