Large study on milk: Risky for women but not for men
Av Ten years ago, researchers at Uppsala University published a study on milk that garnered great attention both in Sweden and globally. The observational study indicated that a high intake of milk was associated with increased mortality, particularly among women.
Karl Michaëlsson, who led the widely discussed 2014 study, is now also the lead author of a new study on the topic of milk.
In this study, approximately 40,000 men and 60,000 women in Sweden were followed for more than 30 years. Shifting from a broad focus on mortality, the researchers have now specifically examined ischemic heart disease (IHD) and acute myocardial infarction (MI). According to Karl Michaëlsson, the study includes a longer follow-up and a refined analysis, incorporating proteomics—a large-scale approach that allowed the researchers to examine multiple proteins simultaneously.
The results of the study showed that the risk of IHD and MI increased for women who consumed large amounts of milk, regardless of fat content. In men with the same milk intake, the researchers found no increased risk.
How much greater did you find the risk to be for women?
– That depends on how you measure it. We essentially measure the rate of progression to myocardial infarction, and with a consumption of 3 glasses per day, we observe approximately a 20% faster progression rate in women, says Karl Michaëlsson.
The researches found that higher intakes of milk in women conferred higher plasma concentrations of the protein ACE2 and lower concentrations of FGF21. Both proteins are well-known cardiometabolic proteins with systemic effects in opposite directions. Higher ACE2 concentrations are a strong risk factor for cardiovascular mortality, while higher FGF21 levels have been shown to prevent cardiometabolic outcomes and extend animal lifespan, the study states.
So, what explains the difference between the sexes?
– We believe it has to do with how the body breaks down milk sugar, and there is a gender difference in this process.
The researchers themselves did not study the breakdown in this study, but instead refer to previous research in the field. They refer to studies that have shown that high blood concentrations of galactose, which is found in milk sugar, can be harmful in large amounts. A high accumulation of galactose can lead to cell stress and inflammation, as well as negative effects on the heart and blood vessels.
– Women break down galactose less efficiently than men. It seems strange that this is the case, but there is a functional advantage. Women need galactose for breast milk production, so it has been an evolutionary benefit during the fertile years. However, when women consume more galactose as they get older, we see that it could instead become a disadvantage.
The participants in the study were born between 1914 and 1952 and self-reported their milk consumption, which the researchers then measured repeatedly over several decades.
Karl Michaëlsson points out that a randomized study would be ideal for drawing more comprehensive conclusions, but it is not feasible to conduct such a study reliably over a long period.
– One always has to include a caveat with this type of study. We haven't been able to randomize milk versus non-milk. This is an observational study, and we are doing the best we can, trying to piece together the puzzle, he says, and continues:
– We can't say it's a direct causal relationship, we see it as one piece of the puzzle. Eventually, we'll have a more complete puzzle, and then we'll try to draw conclusions.
He is also clear that the study is not intended to serve as dietary recommendations.
– I want to leave that to the Swedish Food Agency. My role is to present the research, and after that, independent individuals can draw conclusions.
As for fermented dairy products, such as yogurt, the researchers found no increased risk of IHD or MI.
Why do you think milk generates so much interest?
– On average, Swedes have been high consumers of milk. In the 1950s and 60s, milk was on the table at breakfast, lunch, and dinner. The average consumption was three glasses a day. But over the years, it has decreased, and consumption patterns have changed.
Read the full study, published in BMC Medicine in November:
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