Taking vitamin D supplements does not reduce the risk of depression during middle age or later in life, according to a large study published Tuesday in the Journal of the American Medical Association (JAMA).
Some previous studies have linked low blood levels of vitamin D — sometimes called the “sunshine vitamin” because the body absorbs the nutrient through exposure to sunlight — with a higher risk of late-life depression. For that reason, it was thought that taking vitamin D supplements might serve as a preventive treatment.
No evidence of such an effect was found in the new study, which is one of the largest and longest randomized controlled trials (RCTs) to investigate the topic.
“There was no significant benefit from the supplement for this purpose. It did not prevent depression or improve mood,” says Dr. Oliva Okereke, the study’s lead author and a psychiatrist at Massachusetts General Hospital, in a released statement.
Why the study was done
Preventing late-life depression is a public health priority. The condition is often undertreated in older people. Although vitamin D supplementation has been touted as a possible treatment, prior studies that have suggested its usefulness for that purpose have been primarily observational. Such studies cannot offer definitive answers about a treatment’s effectiveness, for they show only correlations, not causations. Other factors besides vitamin D — ones not addressed in the studies — may explain the results.
RCTs, which are considered the gold standard of medical research, offer a much more rigorous (although not perfect) measure of a treatment’s effectiveness. As background information in the current study points out, 13 RCTs have previously looked at the impact of vitamin D supplements on depression or mood during middle age or later in life. All but one found the supplements had no effect.
Only four of those RCTs, however, had participants take a dose of vitamin D that was 800 IU/day or greater for 12 months or longer. The new study attempts to address those methodological limitations, as well as another one: size.
“One scientific issue is that you actually need a very large number of study participants to tell whether or not a treatment is helping to prevent development of depression,” explains Okereke. “With nearly 20,000 people, our study was statistically powered to address this issue.”
The current study used data collected from 18,353 American men and women who were participating in a larger clinical trial investigating preventive strategies for cardiovascular disease and cancer. All were 50 years or older, and none had clinical signs of the condition when they entered the study.
Half the participants were randomly assigned to receive either 2000 IU of cholecalciferol (vitamin D3) daily, while the other half received a placebo.
The participants were followed for an average of five years, and 90 percent completed the trial. During that time, 609 of those who received the vitamin D and 625 of those who received the placebo developed symptoms of clinical depression — a difference that was statistically insignificant. Nor was there any significant difference between the groups in the participants’ self-reported mood scores during the course of the study.
Interestingly, the study also found no association between low blood levels of vitamin D and a risk of depression or depressive symptoms.
“These findings do not support the use of vitamin D3 in adults to prevent depression,” Okereke and her colleagues conclude.
Limitations and implications
The study has its own limitations. Most notably, it relied on the participants’ self-reports about depressive symptoms and mood. Such reports can be unreliable.
Still, the study’s findings support those from almost all of the smaller RCTs on this topic. They are also in line with a growing body of other research that has found that taking vitamin D supplements in the hopes of preventing various illnesses (including COVID-19) is unnecessary and, in some cases, dangerous.
The National Academy of Medicine has determined that healthy adults (those without a specific disease related to a vitamin D deficiency) need, on average, 600 international units (IUs) of vitamin D daily — until the age of 71, when they need, on average, 800 IUs.
As I’ve noted in Second Opinion before, Vitamin D is unique among micronutrients, as it’s produced in the skin during exposure to sunlight. So although the vitamin can be obtained through food (such as salmon, egg yolks and fortified milk), just five to 30 minutes of sunlight exposure twice a week is usually sufficient to meet most people’s vitamin D needs.
And, yes, that includes people living in Minnesota and other northern latitudes.
FMI: You’ll find an abstract of the new study on JAMA’s website, but the full study is behind a paywall.