“Over” supplementation of vitamin D, referred to as “hypersufficiency,” can slow the progression of frailty, according to a new study with mice.
When it comes to vitamin D, most adults exhibit either frank deficiency, which results in clear clinical symptoms, or insufficiency, which often goes undetected. But, until now, researchers have had difficulty determining how that insufficiency impacts physical health and the vulnerability of older adults to frailty as they age.
“We found that in aged mice, low levels of vitamin D result in physical declines, such as reduced grip strength and grip endurance—the ability to sustain a grip—and that they started developing as soon as one month after reduction of vitamin D intake,” said first author Kenneth L. Seldeen, research assistant professor in the medicine department in the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo.
Just Right Amount of Vitamin D
A key finding of the study was that over the four months of treatment, vitamin D status played an important role in the onset of frailty. The investigators measured frailty in mice based on strategies similar to those used for humans. These strategies define frailty as having three or more of the following: unexpected weight loss, weak grip strength, poor endurance, low activity levels, and slow gait speed.The researchers found that frailty progressed in two groups of the mice where daily vitamin D consumption was either 125 International Units (IU) per kilogram of chow, resulting in an insufficient level, or 1,000 IU per kilogram of chow, which establishes serum levels of vitamin D considered sufficient for a human.
“Only when mice were given the highest amount of vitamin D, at 8,000 IU per kilogram of chow, did frailty not progress over the timeframe of the study,” Seldeen said.
These findings are particularly relevant to the ongoing discussions about how much vitamin D aging adults need to stay healthy. “There is disagreement about what level of vitamin D is considered sufficient for adults.”
Seldeen explains that the National Academy of Medicine (NAM) has identified 20 nanograms per milliliter (ng/ml) of vitamin D in the blood as the level necessary for adults to be vitamin D sufficient, based largely on what they need to maintain bone health. The NAM Food and Nutrition Board has recommended that adults ages 19–70 consume 600 IU of vitamin D per day and that individuals over 70 consume 800 IU of vitamin D per day.
A growing body of literature suggests that vitamin D is important for other aspects of health, and a number of researchers in the field consider 30 ng/ml as the necessary minimum level, said coauthor Bruce R. Troen, professor of medicine, chief of the division of geriatrics and palliative medicine, and director of the Center for Successful Aging.
“The findings of our study suggest that a level of even 30 ng/ml is not enough, and that in fact 60 ng/ml was needed in order to prevent frailty progression in these older mice,” Seldeen said.
That’s the amount that the NAM considers the safe upper limit for vitamin D in the blood, a level that could roughly be achieved with a maximum daily dose of 4,000 IU/day, considered safe by the NAM.
What About Humans?
While this finding is especially intriguing, Seldeen notes that, of course, a single study won’t settle the question.“Unfortunately, higher than standard amounts of supplementation are rarely investigated,” he said. “However, this study raises the possibility of including higher dose groups into future human trials involving vitamin D.”
“Studying the direct impacts of serum vitamin D levels in humans is fairly difficult, as the impacts might take years to manifest and it may not be safe to test the impacts of having persistently low or high vitamin D levels,” Seldeen said. “Using an animal model, we are able to examine these potentially riskier levels of vitamin D and the biological impacts during aging.
“Also, doing so in genetically identical mice all living the same lifestyle, compared to the complexity of human diversity, allows greater focus on the specific effects caused by the different vitamin D levels.”
Additional coauthors are from the Veterans Affairs Western New York Healthcare System and the University at Buffalo. The Veterans Affairs Rehabilitation Research and Development, the National Institutes of Health, and the Indian Trail Foundation funded the work.
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