Drinking non-fermented milk may increase the risk of heart disease in women

Researchers analyzed data from over 100,000 Swedish adults over 33 years, though the study couldn’t confirm a direct cause-and-effect link.

In a recent study published in BMC Medicine, Swedish researchers explored the link between fermented and non-fermented milk consumption and heart health, specifically ischemic heart disease and myocardial infarction risk. Using data from two large Swedish cohort studies, the study examined the association between milk consumption and cardiometabolic protein patterns in the blood.

Background

Ischemic heart disease results primarily from restricted blood flow to the heart and is a significant global health issue and a major cause of early mortality. Although research indicates that cardiovascular health is influenced by multiple factors, including diet, the role of dairy products, especially milk, remains ambiguous.

Furthermore, different types of milk products, such as non-fermented fresh milk or fermented milk products such as yogurt, may affect heart health in distinct ways, possibly due to variations in the microbial content or bioactive compounds formed during fermentation.

Although milk is widely recommended as part of a balanced diet for its calcium, vitamin D, and protein content, studies on its cardiovascular impact have reported conflicting results. Some research suggests that high milk consumption might increase cardiovascular risks, while others find no link or even protective effects.

About the study

In the present study, the researchers aimed to clarify the impact of milk consumption on cardiovascular health, focusing on fermented and non-fermented milk intake and their potential effects on specific blood proteins related to heart disease. They analyzed data from two Swedish cohort studies, the Cohort of Swedish Men (COSM) and the Swedish Mammography Cohort (SMC), which cumulatively involved over 100,000 participants who were monitored for up to 33 years.

The participants were required to complete dietary and lifestyle questionnaires, which included details on milk consumption, categorized into non-fermented and fermented types. Additionally, blood samples were taken to assess cardiometabolic proteins. The researchers excluded participants who had a history of ischemic heart disease or cancer, and the final dataset consisted of over 40,000 men and close to 60,000 women.

Dietary intake was assessed through validated food frequency questionnaires, with milk intake specified by fat content (0.5%, 1.5%, or 3%) and type (non-fermented versus fermented). The total milk intake was calculated by combining the servings across types and fat contents. High-throughput immunoassays were used to measure the protein concentrations in blood, focusing on 276 proteins related to cardiometabolic health.

The study employed Cox proportional hazards regression models to evaluate the association between milk intake and the risk of ischemic heart disease or myocardial infarction, adjusting for factors such as age, physical activity, dietary habits, alcohol intake, and socioeconomic status. The analysis also assessed dose-response relationships for milk intake, with stratified analyses to explore potential modifiers like sex and lifestyle. Sensitivity analyses excluded the participants with comorbidities and assessed impacts across different intake levels and fat contents.

Results

The study found that increased consumption of non-fermented milk was associated with an elevated risk of ischemic heart disease and myocardial infarction in women but not in men. Specifically, women who consumed more than 300 mL of non-fermented milk (equating to 2 or more glasses) daily showed a significant increase in ischemic heart disease risk, with the hazard ratio increasing progressively with higher intake.

Furthermore, this association was consistent across all milk fat percentages (0.5%, 1.5%, and 3%) and was significant even after adjusting for lifestyle and dietary factors. In contrast, fermented milk intake was not linked to ischemic heart disease or myocardial infarction risk in either sex.

The study also found that women who consumed high amounts of non-fermented milk exhibited distinct patterns in cardiometabolic proteins. Higher intake of non-fermented milk was found to correlate with elevated levels of angiotensin-converting enzyme 2 (ACE-2), a protein that was associated with cardiovascular risks.

Additionally, the levels of fibroblast growth factor 21 (FGF21), a protein that is protective against cardiometabolic conditions, were found to be lower in women who consumed non-fermented milk in large amounts. These protein changes may reflect underlying biological pathways affected by non-fermented milk consumption, potentially explaining the higher ischemic heart disease risk observed in women.

Moreover, substitution analysis indicated that replacing non-fermented milk with fermented milk or fermented milk products such as yogurt could potentially lower the risk of ischemic heart disease, although further research is needed to confirm this possibility.

Conclusions

Overall, the study suggested that non-fermented milk, irrespective of fat content, may contribute to higher ischemic heart disease risk in women through pathways involving ACE-2 and FGF21.

The findings highlighted a potential sex-specific risk of ischemic heart disease associated with non-fermented milk intake, with a greater risk in women who consume large amounts of fresh milk. The study warranted further investigation into fermented milk products as a potentially safer dairy alternative.