Vitamin A is a vital nutrient that supports the body's development and strengthens the immune
system. Because our bodies do not naturally produce vitamin A, some choose to take
supplements. However, too much vitamin A is likely to harm bone health, researchers warn.
Normally, we derive vitamin A from the food we eat, such as carrots, sweet potatoes, beef liver,
salmon, and dairy products.
For example, half a cup of raw carrots contains about 573 mcg RAE, and 3 ounces of pan-fried
beef liver contain 6,582 mcg RAE (about 7 times more than the daily recommended dose)
according to the NIH.
Despite the fact that we can derive enough vitamin A from food, some individuals choose to
boost their levels of vitamin A by taking supplements.
However, over time, this might lead to an overload of this nutrient, which can actually increase a
person's risk of experiencing bone fractures. This is what researchers from the Sahlgrenska
Academy at the University of Gothenburg in Sweden have found in a recent study.
The study's results — reported in the Journal of Endocrinology — indicate that taking too much
vitamin A can make bones "thin out," thereby putting them at risk of fracturing easily.
The researchers conducted the study in mice, and it came on the heels of another project that also
looked at the effect of over-supplementing vitamin A on bone health.
Previous studies in mice, the study authors explain, have tested the effects of short-term vitamin
Those studies found that rodents that took the equivalent of 13–142 times the recommended
daily amount of vitamin A for humans had poorer bone health and an increased risk of fracturing
after only 1 or 2 weeks.
This time, though, the team wanted to test vitamin A over-supplementation in conditions that
more closely resembled those to which a person may be exposed when taking supplements over
long periods of time.
So, study co-author Dr. Ulf Lerner and team administered lower vitamin A doses — the
equivalent of 4.5–13 times the recommended daily allowance for humans — for 1, 4, or 10
The scientists saw that after only 8 days of over-supplementation, the mice's bone thickness had
started to decrease. Over 10 weeks, the rodents' bones became increasingly fragile and prone to
"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," explains
"In our study," he adds, "we have shown that much lower concentrations of vitamin A, a range
more relevant for humans, still decreases rodent bone thickness and strength."
In the future, Dr. Lerner and team would like to see whether over-supplementation of vitamin A
can also impact bone growth related to exercise, as well as the effects of overdosing in older
mice, hoping to simulate the impact of too much vitamin A in aging humans.
"Overconsumption of vitamin A may be an increasing problem as many more people now take
vitamin supplements," warns Dr. Lerner. "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."