A new study, undertaken in mice, 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, and suggests that people should be cautious of over-supplementing vitamin A in their diets.

Vitamin A is an essential vitamin that 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.

In this study, Dr Ulf Lerner and colleagues from Sahlgrenska Academy at the University of Gothenburg, report that mice 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 8 days, which progressed over the ten-week study period.

Dr. Ulf Lerner commented, "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. 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."

"Overconsumption of vitamin A may be an increasing problem as many more people now take vitamin supplements. An overdose of vitamin A could be increasing the risk of bone weakening disorders in humans but more studies are needed to investigate this. In the majority of cases, a balanced diet is perfectly sufficient to maintain the body's nutritional needs for vitamin A," cautioned Lerner. The full findings are present in the Journal of Endocrinology.