Excessive vitamin A increases risk of bone fractures

Excessive vitamin A consumption may decrease bone thickness, leading to fractures

Consuming too much vitamin A may decrease bone thickness, leading to weak and fracture prone bones, according to a study published in the Journal of Endocrinology.

Why Vitamin A is important

Vitamin A is an essential vitamin that is important for numerous important functions involved in  regulation of growth, skin and eyesight, immunity, reproduction and bone health. Vitamin A is a group of fat-soluble substances that are found in animal products (as retinol and retinal). Vitamin A also includes carotenoids, which are produced by plants. 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. The recommended daily amount of vitamin A is 900 micrograms (mcg) for adult men and 700 mcg for adult women.

Dangers of overdose

Past studies in mice have shown that short-term high dose of vitamin A (equivalent of 13-142 times the recommended daily allowance), results in decreased bone thickness and an increased fracture risk after just 1-2 weeks. This study was undertaken to examine the effects of lower vitamin A doses that are nearby to those consumed by people taking supplements, over longer periods of time.

much lower concentrations of vitamin A, a range more relevant for humans, still decreases rodent bone thickness and strength

Researchers found that mice given lower doses of vitamin A, equivalent to 4.5-13 times the recommended daily allowance (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.

“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,” said lead author, from Sahlgrenska Academy at the University of Gothenburg.   

Dr Ulf Lerner cautioned, “Overconsumption of vitamin A may be an increasing problem as many more people now take vitamin supplements. 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.”