Web edition: August 27, 2010
The reputations of milk, cheese and many other dairy products have taken a bit of a hit in recent years for their constituting a major dietary source of saturated fats — a risk factor for cardiovascular disease. How ironic, then, that a Swedish study now correlates intake of dairy fats with a reduced risk of heart attacks.
The new data don’t actually demonstrate that dairy fats confer any protection. They merely serve as markers of dairy intake since their sole source is ruminant animals, such as cows. Those diagnostic fats simply argue that one or more facets of dairy foods diminish heart-attack risk — especially in women.
Eva Warensjö of Uppsala University and her colleagues analyzed health, diet and other lifestyle data — such as regular exercise or a history of smoking — that had been collected between 1987 and 1999 from participants of three ongoing studies. Two of the health studies had included both genders. The other, a local mammography screening project, obviously involved just women.
By Jan. 1, 2000, 696 individuals within these groups had developed a first heart attack. Depending on gender, one man or two women who remained heart-attack-free within these studies were randomly selected for comparison. Each was roughly the same age, the same gender, came from the same general part of Sweden and started the study at the same time as the heart-attack patient to whom he or she was compared.
Concentrations of the dairy-specific fats pentadecanoic acid, abbreviated 15:0, and heptadecanoic acid, aka 17:0, were measured in blood samples that had been archived from each individual. The higher the circulating concentrations of these fats in a woman’s blood, the lower her risk of developing a first heart attack, Warensjö and her colleagues report in the July American Journal of Clinical Nutrition. A similar trend, though not statistically significant, showed up in men.
Taking into account such heart risk factors as obesity, high blood pressure and elevated cholesterol diminished the association between dairy fats and heart attacks, also known as myocardial infarctions. But Warensjö says that makes sense since it’s likely that those other risk factors are manifestations of changes that might be affected by dairy consumption. For instance, several studies have linked relatively high intakes of dairy foods with lower blood pressure.
Dairy intake differed between men and women — not only by amount but also by type. Women who remained heart-attack-free tended to eat more cheese, men to consume more fermented dairy goods, like yogurt and kefir. And milk: In this study, people who had and who hadn’t suffered a heart attack regularly downed exactly the same amount.
The researchers did not sort dietary intakes on the basis of a food's total fat content, so there’s no way to identify whether skim milk proved healthier than whole, or low-fat cheeses proved heart healthier than higher fat ones. At least in this study. And too bad, because it would have been nice to identify any selective benefits in low- versus moderate- or high-fat dairy goods. Then again, if Swedes tend to be rather homogenous in their diet, there may be too few people eating the really low- or high-fat fare to make any statistically significant assessments from those data.
For now, Warensjö says, “I strongly believe that what we are seeing is not just a dairy-fat effect. I suspect it’s more a dairy-food effect.”
There’s a lot more to cow’s milk than fat and protein. It contains hundreds of trace nutrients, hormones, and other materials too. And the Uppsala epidemiologist says that these — alone or, more likely, in combination as part of a dairy food — likely explain the apparent dairy benefit that her team has just reported.
E. Warensjö, et al. Biomarkers of milk fat and the risk of myocardial infarction in men and women: A prospective, matched case-control study. American Journal of Clinical Nutrition, Vol. 92, July 2010, p.194. doi:10.3945/ajcn.2009.29054
A. Brevik, et al. Evaluation of the odd fatty acids 15:0 and 17:0 in serum and adipose tissue as markers of intake of milk and dairy fat. European Journal of Clinical Nutrition, Vol. 59. December 2005, p. 1417.