Low levels of vitamin D could lead to depression in otherwise healthy women, according to a recent study.

Vitamin D is an essential nutrient for bone health and muscle function. Deficiency has been associated with impaired immune function, some forms of cancer and cardiovascular disease.

Researchers at Oregon State University found that young women with lower levels of vitamin D were more likely to have clinically significant depressive symptoms over the course of a five-week study. The results were consistent even when researchers took into account other possible explanations, such as time of year, exercise and time spent outside.

"Depression has multiple, powerful causes and if vitamin D is part of the picture, it is just a small part," David Kerr, lead author of the study, said in a statement. "But given how many people are affected by depression, any little inroad we can find could have an important impact on public health."

For the study, researchers recruited 185 college students, all women ages 18-25, to participate in the study at different times during the school year. Vitamin D levels were measured from blood samples and participants completed a depression symptom survey each week for five weeks.

Many women in the study had vitamin D levels considered insufficient for good health, and the rates were much higher among women of color, with 61 percent of women of color recording insufficient levels, compared to 35 percent of other women. In addition, more than a third of the participants reported clinically significant depressive symptoms each week over the course of the study.

"It may surprise people that so many apparently healthy young women are experiencing these health risks," Kerr said.

As expected, the women's vitamin D levels depended on the time of year, with levels dropping during the fall, at their lowest in winter, and rising in the spring. Depression did not show as a clear pattern, prompting Kerr to conclude that links between vitamin D deficiency and seasonal depression should be studied in larger groups of at-risk individuals.

The findings are detailed in the journal Psychiatry Research.