For people with established cardiovascular disease (CVD), greater consumption of various dairy products was associated with worse health outcomes in a Norwegian study.
Rising daily intakes of total dairy and milk were each significantly associated with increased risks of stroke, cardiovascular mortality, and all-cause mortality over follow-up generally spanning 5 to 14 years in patients with stable angina, according to clinical dietitian Vegard Lysne, PhD, of University of Bergen and Haukeland University Hospital, and colleagues.
Acute myocardial infarction (MI) had no clear linear relationship with total dairy intake or milk consumption, but the risk was increased with butter exceeding 2 g/1,000 kcal in a person’s daily diet.
Likewise, data were inconclusive regarding cheese consumption and cardiovascular risk, as higher cheese intake had no significant associations with acute MI, stroke, CVD mortality, or all-cause mortality, the study authors reported in the European Journal of Preventive Cardiology.
Thus, the study draws a more complicated picture of dairy’s risks that supports other observational data suggesting that different dairy products may have different effects. “We can speculate that at least part of the differential associations seen for milk, butter, and cheese may be because cheese contains intact MFGM [milk fat globule membrane], while milk and butter does [sic] not,” Lysne’s team wrote.
Yet overall, dairy is “probably harmful,” the cheese verdict unclear, and some of the fermented dairy products may be less dangerous if dairy is to be consumed at all, commented Andrew Freeman, MD, a cardiologist at National Jewish Health in Denver, who was not involved with the study.
Even without a randomized trial, Freeman said in an interview, “there’s enough signal in the noise to draw the conclusion that higher-fat dairy products, the number one source of saturated fat in our diet, are probably not going to be helpful to human health, and heart health in particular.”
He cautioned that there may be worldwide variation in dairy’s effects, however. Dairy products may be different between countries that place more restrictions on raising cattle with certain chemicals, like growth hormones, and those that don’t. For instance, the U.S. permits recombinant somatotropin treatment of dairy cows, unlike the European Union, Australia, and Japan.
Nevertheless, the large PURE study of people around the world consistently found the best clinical outcomes in those who ate a balanced diet including lots of fruits and vegetables and a modest amount of dairy, unprocessed red meat, and nuts and legumes. The PURE investigators had separately challenged the association of fats (including saturated fats) with mortality and also reported that compared with no dairy, eating at least two servings of it per day was linked with less CVD and mortality.
Current U.S. dietary guidelines recommend a few servings of low-fat or fat-free dairy per day. There is no mention of specific products except to discourage the consumption of cream, sour cream, and cream cheese due to their low calcium content.
“Dairy is a heterogenous food group with divergent health effects and dairy products should therefore be investigated individually,” Lysne and colleagues maintained.
Their analysis was based on 1,929 patients with stable angina (80% men, mean age 62 years) from the Western Norway B Vitamin Intervention Trial.
All had undergone coronary angiography due to suspected coronary artery disease or aortic stenosis in 1999-2004. Use of preventive medications was high and included aspirin (90%), statins (90%), and beta-blockers (77%).
Participants self-reported dietary habits on a food frequency questionnaire. Average dairy intake was reportedly 169 g/1,000 kcal; the main component was generally milk (133 g/1,000 kcal).
The study’s observational nature left room for bias and confounding when assessing the relationship between dairy consumption and CVD risk.
Indeed, Lysne’s group found that people who ate more dairy tended to eat less meat, vegetables, fruit and berries, fish, and potatoes. These individuals also gained more calories from protein and less from fats (except saturated fats).
Other study limitations include the lack of additional dietary evaluations over years of follow-up and the potential for participants to mischaracterize their diets on a survey. Additionally, the results may have limited generalizability to the general population and people in other settings, the study authors acknowledged.
Lysne and Freeman disclosed no conflicts of interest.