Vitamin D can come from sun as well as food and supplements. Possibly for this reason, people are often warned against getting too much of this essential nutrient; more, in this case, is not better. Now, researchers at the University of California, San Diego, School of Medicine have uncovered an unexpected downside to getting too little of this nutrient. People with lower blood levels of vitamin D, they discovered, were twice as likely to die prematurely as those with higher levels. “This confirms observations from the National Academy of Sciences — Institute of Medicine Committee to Review Dietary Reference Intakes for Vitamin D and Calcium that concentrations less than 20 ng/mL [in the blood] are too low for safety,” wrote the authors in their study.
The Sunshine Vitamin
Most people are able to meet all of their vitamin D needs by directly exposing their skin to the sun and eating a healthy diet. Vitamin D, which is found in cells throughout the body, helps the body absorb calcium, which is central to bone health. Yet it also is required by muscles, nerves, and the immune system. Once you’ve passed out of infancy, the Institute of Medicine (IOM) recommends you take 600 international units each day until the age of 71, when you should increase that amount to 800. IOM also recommends adults never exceed 4,000 international units per day, which might raise blood levels too high.
For the current study, Dr. Cedric Garland, professor in the Department of Family and Preventive Medicine and his co- researchers investigated the findings of the IOM by searching biomedical databases for articles that analyzed vitamin D, blood levels, and mortality rates between the years 1966 through 2013. They identified 32 studies analyzing the primary form of vitamin D found in blood and pooled all the data. The studies, taken together, included a total of 566,583 participants from 14 countries.
What did the researchers find? People whose vitamin d blood level concentrations were in the lowest fifth had nearly twice the death rate as those in the highest fifth. The researchers also noted that a full two-thirds of the U.S. population have an estimated blood level below the cut-off point.
"This study should give the medical community and public substantial reassurance that vitamin D is safe when used in appropriate doses up to 4,000 International Units (IU) per day," Dr. Heather Hofflich, professor in the UC San Diego School of Medicine's Department of Medicine, stated in a press release. That said Hofflich advises adults get tested by their doctors and discuss the results. Turns out either too little or too much may be dangerous when it comes to the sunshine vitamin.
Source: Garland CF, Kim J, Mohr SB, et al. Meta-analysis of All-Cause Mortality According to Serum 25-Hydroxyvitamin D. American Journal of Public Health. 2014.