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23.08.2022

Milk may be a risk factor for depression, yogurt and kefir are not

A high intake of dairy may increase the risk of depression. At least, when it comes to non-fermented forms of dairy. Fermented dairy varieties such as yogurt, buttermilk and kefir actually lower the risk of depression.

Study
Australian epidemiologists at Deakin University analyzed data from 2,603 Finnish men collected in the Kuopio Ischaemic Heart Disease Risk Factor Study. That study began in the 1980s. The study participants were 42-60 years old at the time.

The men had kept a record of what they ate, on the basis of which the researchers determined their intake of dairy. They distinguished between non-fermented dairy, such as milk and custard, and fermented dairy, such as buttermilk, yogurt, kefir and cheese.

Based on their intake, the researchers divided the men into 3 groups or tertiles of approximately equal size. The men in the first tertile had the lowest intake, the men in the third tertile had the highest intake.

The researchers followed the men for 26 years. They had access to the men's medical records and could determine whether the men had been diagnosed with depression.

Results
The researchers were unable to find any effect of total dairy intake on depression. But when they distinguished between fermented and non-fermented dairy, they did find a statistically significant association.

The men with the highest intake of non-fermented dairy were twice as likely to have depression than the men with the lowest intake of non-fermented dairy. That difference was statistically significant.

The men with the highest intake of fermented dairy were 30 percent less likely to be diagnosed with depression than the men in the tertile with the lowest intake. You can see this above. The differences between the groups were not statistically significant.

When the researchers omitted cheese and only looked at other fermented dairy products, the protective effect of a high intake increased to 38 percent and was statistically significant.

Mechanism
The researchers propose a number of possible explanations for the associations they found. One is that non-fermented dairy contains lactose. Galactose is a disaccharide, and one of them is galactose. In animal experiments, sugar accelerates aging processes. In addition, it damages brain cells. Fermented dairy contains little galactose because bacteria have converted it.

Another suspect is the protein in dairy. Many cows produce the protein A1 beta casein. That protein changes in the body into the peptide beta-casomorphin-7 [BCM-7; structural formula below].

Some nutrition scientists suspect that BCM-7 may damage the brain. If they are right, then that problem hardly arises, if at all, with fermented dairy. The fermentation process cuts beta casein proteins into smaller pieces that can no longer act as a BCM-7 precursor.

Conclusion
"If corroborated by future research, including moderate amounts of fermented dairy products (e.g., sour milk, kefir, yogurt) while limiting intake of nonfermented dairy products (e.g., milk) could form part of dietary recommendations for the prevention of depression", summarize the researchers.

"To confirm findings observed in this study, prospective studies that include repeated measures of diet and are conducted in different populations and sexes are required."

Source:
J Nutr. 2022 Aug 9;152(8):1916-26.

More:
How dietary flavonoids and carotenoids protect against depression 04.01.2022
Fruits and vegetables are natural antidepressants 28.04.2020
Healthy diet protects against depression 05.03.2019

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