Higher vitamin intake may appear to be associated with fewer depressive symptoms, but most of these relationships disappear once differences in people’s health, socioeconomic circumstances, and behavior are considered, according to a study published in the Journal of Affective Disorders.
Vitamins perform numerous functions that could plausibly affect mental health. Vitamins B6, B9, and B12 contribute to processes involved in producing or regulating chemical messengers in the brain. Vitamins C and E help protect cells from potentially damaging molecules, while vitamin D may influence brain signaling and immune activity.
Previous studies have linked low levels of certain vitamins with depression, raising the possibility that improving nutrition could help prevent or reduce symptoms. However, the evidence has been inconsistent. People with higher vitamin intake may also differ in income, education, physical health, smoking, and other characteristics that independently affect depression risk.
The researchers therefore investigated whether vitamins remained associated with depression after considering these broader differences.
Led by Neil Mistry at Georgia Southern University, the team analyzed data from 26,170 adults (13,294 women, with an average age of 47.6 years) who participated in the National Health and Nutrition Examination Survey between 2005 and 2014.
Participants completed the nine-item Patient Health Questionnaire, a widely used measure producing a depression-symptom score from zero to 27. Of the participants, 75.35% had scores below five. Mild symptoms were recorded in 15.54%, moderate symptoms in 5.60%, moderately severe symptoms in 2.48%, and severe symptoms in 1.02%.
Intake of vitamins A, C, D, and E was estimated by asking participants what they had consumed during the preceding 24 hours. Vitamins B6, B9—also known as folate—and B12 were assessed using blood samples. The researchers also constructed an exploratory score intended to represent overall nutrition.
Initial analyses suggested that higher levels of several vitamins were associated with lower odds of depressive symptoms. Vitamins C, D, and E, for example, were inversely associated with having a score of at least five before other factors were considered. However, these associations were no longer statistically significant after adjustment for age, sex, education, poverty, race, body mass index, health limitations, alcohol intake, and tobacco use.
A similar pattern emerged for more serious symptoms. Apparent relationships involving vitamins A and E weakened after adjustment. Vitamin B12 was not consistently associated with depression, and the overall nutritional score also showed no independent relationship.
Vitamin B6 provided an exception. Higher blood concentrations were associated with lower odds of scoring 15 or above, indicating at least moderately severe symptoms, after the researchers adjusted for other factors. The estimated change associated with each additional unit of B6 was small, however, and should not be interpreted as proof that B6 prevents or treats depression.
As the authors concluded, “These findings do not support strong independent associations between vitamin intake and depression presence or severity after accounting for confounding factors.”
The results instead suggest that some apparent vitamin–depression relationships may reflect wider patterns. Greater depression severity was also associated with lower income, lower educational attainment, poorer self-rated health, physical or sleep limitations, tobacco use, and being unmarried. These circumstances can influence both diet and mental health.
Some limitations are to be noted. For instance, the models did not account for antidepressants, other psychiatric medications, or supplements. Moreover, one day of recalled food intake may poorly represent a person’s normal diet.
The study, “Associations between vitamin intake and depression severity: A cross-sectional analysis of NHANES 2005–2014,” was authored by Neil Mistry, Logan T. Cowan, Hani M. Samawi, Amenah Qotineh, Ousainou Gomez, and Kelly L. Sullivan.