Consuming too much Vitamin A may decrease bone thickness: Study

Consuming too much vitamin A may decrease bone thickness, leading to weak and fracture-prone bones, according to a study conducted in mice.

The study, published in the Journal of Endocrinology, found that sustained intake of vitamin A, at levels equivalent to 4.5-13 times the human recommended daily allowance (RDA), caused significant weakening of the bones.

It suggests that people should be cautious of over-supplementing vitamin A in their diets, said researchers at the University of Gothenburg in Sweden.

Vitamin A is important for numerous biological processes including growth, vision, immunity and organ function.

Our bodies are unable to make vitamin A but a healthy diet including meat, dairy products and vegetables should be sufficient to maintain the body's nutritional needs.

Some evidence has suggested that people who take vitamin A supplements may be increasing their risk of bone damage, researchers said.

Previous studies in mice have shown that short-term overdosing of vitamin A, at the equivalent of 13-142 times the recommended daily allowance in people, results in decreased bone thickness and an increased fracture risk after just 1-2 weeks, they said.

This study is the first to examine the effects of lower vitamin A doses that are more equivalent to those consumed by people taking supplements, over longer time-periods.

Mice were given lower doses of vitamin A, equivalent to 4.5-13 times the RDA in humans, over a longer time period, also showed thinning of their bones after just eight days, which progressed over the ten-week study period, researchers said.

"Previous studies in rodents have shown that vitamin A decreases bone thickness but these studies were performed with very high doses of vitamin A, over a short period of time," said Ulf Lerner from the University of Gothenburg.

"In our study, we have shown that much lower concentrations of vitamin A, a range more relevant for humans, still decreases rodent bone thickness and strength," Lerner said.

Researchers intend to investigate if human-relevant doses of vitamin A affect bone growth induced by exercise, which was not addressed in this study.

They will also study the effects of vitamin A supplementation in older mice, where the growth of the skeleton has ceased, as is seen in the elderly.

(With inputs from agencies.)