Researchers suggest that a higher intake of low-fat milk and yogurt may reduce the risk of developing symptoms of depression.
In a study of more than 1,000 adults from Japan, researchers found that those who consumed a higher amount of low-fat milk and yogurt were less likely to develop symptoms of depression, compared with those who consumed lower amounts of these dairy products.
Study co-author Prof. Ryoichi Nagatomi, of Tohoku University in Japan, and colleagues recently reported their results in the journal Social Psychiatry and Psychiatric Epidemiology.
Depression - also referred to as major depressive disorder - is one of the most common mental health disorders in the United States.
According to the National Institute of Mental Health, in 2015, around 16.1 million adults in the U.S. had experienced at least one episode of major depression during the previous 12 months.
While symptoms of depression vary from person to person, they may include persistent sadness, feelings of hopelessness, guilt, or helplessness, irritability, fatigue, problems sleeping, and thoughts of death or suicide.
Prof. Nagatomi and colleagues note that previous studies have associated dairy intake with depression, though whether the effect is positive or negative has been inconclusive.
For their study, the researchers set out to investigate how the consumption of certain low-fat and high-fat dairy products individually impact the risk of developing symptoms of depression.
Low-fat dairy intake linked to lower prevalence of depressive symptoms
The research included 1,159 adults from Japan aged between 19 and 83 years, the majority of whom were women.
Participants disclosed how often they consumed low-fat and whole-fat milk and yogurt in a dietary questionnaire. The intake of cheese, butter, and other dairy products was not reported.
Symptoms of depression were assessed using the 20-item self-rating depression scale.
The team identified depressive symptoms among 31.2 percent of men and 31.7 percent of women.
Compared with adults who reported no consumption of low-fat dairy products, those who consumed low-fat milk and yogurt between one and four times weekly were less likely to have symptoms of depression.
These results remained after accounting for a number of possible confounding factors, such as age, sex, overall diet and lifestyle, and health status.
Commenting on what their findings show, the researchers say:
"The current results indicate that a higher frequency of low-fat dairy consumption may be associated with a lower prevalence of depressive symptoms."
No link was identified between the consumption of whole-fat dairy products and depression. The researchers hypothesize that this may be because the trans-fatty acids in whole-fat milk - which are associated with depression - were offset by an amino acid in milk, called tryptophan.
The team concludes that further studies are needed to pinpoint the mechanisms underlying the link between low-fat dairy intake and a lower risk of depression.