The Grapevine

Vitamin A Is Unhealthy, If Consumed In Excess

Vitamin A is an important nutrient. Apart from regulating cell growth, the fat-soluble vitamin also promotes better vision and immunity. But is it possible to consume too much of it?

The recommended intake of the nutrient is 900 micrograms for adult men and 700 micrograms for adult women. Eggs, meat, fish oils, leafy greens, beef liver, cheese, and fortified milk make up some of the top dietary sources of the vitamin.

Certain groups like vegetarians or alcoholics, who are prone to deficiencies, might require extra Vitamin A, according to the National Institutes of Health. This may also apply to people with conditions like liver diseases, cystic fibrosis, and Crohn's disease.

But overall, vitamin A deficiencies are considered rare in the United States, especially compared to developing countries. Consuming too much of it, on the other hand, is possible when people use supplements, also known as retinol.

"Overconsumption of vitamin A may be an increasing problem as many more people now take vitamin supplements," said Dr. Ulf Lerner from the University of Gothenburg, Sweden.

Lerner and colleagues recently published findings from a rodent study, revealing that excess consumption of vitamin A could decrease bone thickness and elevate the risk of fractures.

"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," Lerner noted.

In the new study, the research team used much lower concentrations of vitamin A in a range more relevant for human beings. But even at this dose, the rodents still experienced a decrease in bone thickness and strength.

"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," Lerner added.

But the potential impact does not stop at bone health. Consuming over 10,000 micrograms of the vitamin in supplement form can also raise the risk of liver damage, headaches, nausea, and skin irritation. 

It is also advisable for pregnant women (who are not a part of vitamin A–deficient populations) to speak to doctors about supplementation since past studies have found associations with birth defects.

"Vitamin A plays an essential role during fetal development; however, if consumed at high doses it can produce teratogenic effects," states one paper.

As many recent studies have suggested, most of us are better off getting our nutrients from food rather than supplements. Taking the latter, even for the antioxidant benefits of vitamin A, may not offer the same benefits as its naturally occurring equivalent.