An international study on vitamin D supplements and depression found the pills could alleviate depression symptoms.
The report's lead author said the study is inconclusive and better research on the topic is needed.
Too many vitamin D supplements can lead to toxicity, which could cause hospitalization.
Vitamin D supplements could alleviate depression symptoms — but taking too many can cause vomiting and other health problems.
A meta-analysis of 41 previous studies on vitamin D, conducted by Finnish, Australian, and US researchers, found that supplements usually helped alleviate symptoms of depression more than a placebo. The analysis is the largest one published on vitamin D supplements and depression so far.
The study's findings contradict the results of a trial that included 18,000 participants. That report, published in 2020 in the Journal of the American Medical Association (JAMA), found no significant difference in rates of depression symptoms between people who took vitamin D and those who didn't.
Both studies have their flaws. The 2020 study followed real people for five years, but it's hard to perfectly control a person's nutrient intake to monitor the effects of vitamin D alone. The new study encompasses much more data, but the people had a range of different health conditions and meta-analyses aren't a gold standard of research.
However, while doubts are brewing about whether vitamin D really is a wonder supplement, the lead author of the new study, PhD candidate Tuomas Mikola, said they are important.
"These findings will encourage new, high-level clinical trials in patients with depression in order to shed more light on the possible role of vitamin D supplementation in the treatment of depression," Mikola, of the University of Eastern Finland, said in the report.
Too many vitamin D supplements can land you in the hospital
But taking too many vitamin supplements can cause health problems.
Excess vitamin D supplements can cause toxicity, or when the nutrient reaches a concentration of at least 150 nanograms per milliliter (ng/ml) in a person's blood.
The rate of people exposed to vitamin D toxicity increased by 1,600% between 2005 and 2011, according to US Poison Control data.
A man in the UK was hospitalized for eight days after taking more than 80 times the recommended daily vitamin D. The supplements, provided to him by a private nutritionist, caused him to keep vomiting and lose 28 pounds in three months.
Another man experienced permanent kidney damage after overdosing on vitamin D supplements.
"It can take a year — or more, sometimes — for things to normalize," Dr. Kendall Moseley, medical director of the Johns Hopkins Metabolic Bone & Osteoporosis Center, told CNBC. "In really extreme cases, patients have to go on dialysis," Moseley says. "It's much harder to fix excess vitamin D than to fix low vitamin D."
If you have a deficiency, nutrition and epidemiology experts previously told Insider to seek a physician's advice on how much of the supplement to take. The National Institutes of Health recommends healthy adults get 600 international units (IU) of vitamin D per day.
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