Vitamin A and Brittle Bones: is there any Truth to the Media Reports?
CNN and various newspapers, including The New York Times and the Houston Chronicle, recently reported on a Swedish study (The New England Journal of Medicine, January 2003; 348: 287-294, 347-349) linking Vitamin A with an increased risk of fractures in aging men. These reports have led many people to wonder if supplements containing Vitamin A are safe, and many media outlets are advising readers against the use of any Vitamin A.
Since I often recommend cod liver oil (which does in fact contain Vitamin A) and other Vitamin A supplements, I was very puzzled by these reports and read the study in its entirety. I was surprised to see how little is known about the participants in the study. Basically all that was recorded was their level of Vitamin A in blood and the incidence of fractures over a thirty-year period. To conclude with certainty from this scant information that Vitamin A is dangerous seems quite a stretch to me.
Before we start thinking of Vitamin A as hazardous, let’s remember that it plays many important roles, including in vision, cell differentiation, early fetal development, immunity, taste, appetite and growth. Vitamin A is an important antioxidant and may have anticancer and antiviral actions. Signs of deficiency include night blindness, acne and other skin conditions, reduced immunity, chronic viral conditions, complications from measles and, conceivably from the measles vaccine.
The US RDA (recommended daily allowance) for Vitamin A is 5,000 IU (international units) a day for adults and proportionately less for children. The most important recognized risk of Vitamin A is that doses exceeding 10,000 units a day in pregnant women were associated with a higher risk of certain birth defects in one study (Lancet 1988;1:236). However, another study found such doses to be associated with a reduction of the same type of birth defects (Lancet 1996;347:899-900). In total there have been fewer than 20 cases reported worldwide of birth defects possibly caused by Vitamin A overdose.
In numerous studies, doses far greater than the RDA were found to be both safe and effective. Doses of 400,000 units a day for 5 months in adolescents with acne were found to be effective and caused no side effects (Int J Dermatol 1981;114:1776 and Br Med J 1963;2:294). The short-term administration of doses of 200,000 to 400,000 units in small children were also studied, and were found to reduce the occurrence of complications from measles and pneumonia while enhancing immunity, again with no side effects reported. Incidentally, the benefits were documented both in children who were deficient in Vitamin A as well as in children who were not (J Trop Pediatr 2002;48(2):72-7, Clin Infec Dis 1994;19(3):489-99, Am J Epidemiol 1997;146(8):646-54, and many other published studies. You may e-mail me for a full list).
Interestingly, this most recent study linking Vitamin A with fractures in aging individuals was performed in Sweden, a country not known for its abundant sunshine. Since we know without a doubt that Vitamin D is associated with bone health and that much of our intake of Vitamin D comes from the sun, it is possible that Vitamin D deficiency is rampant in Sweden. This may explain why Scandinavians in general have higher rates of fractures in comparison to other Europeans.
One possible explanation of why fracture rates were higher in the study participants who had more Vitamin A in their blood is that vitamins A and D need to be balanced. Everything in nature is a matter of balance, and excessive intake of Vitamin A without enough Vitamin D may cause a relative Vitamin D deficiency, possibly leading to brittle bones.
Cod liver oil is apparently a very popular supplement in Sweden, and some experts suggested that the individuals with high levels of Vitamin A in their blood may have consumed ample doses of cod liver oil, over many decades, and this may have depleted them of Vitamin D.
Cod liver oil actually contains both vitamins A and D, but is tilted towards Vitamin A. It is plausible that consuming it without being exposed to sufficient sunshine or taking additional Vitamin D explains the results of this study. This theory may be the best we have, but is not entirely convincing since cod liver oil, in spite of its high Vitamin A to Vitamin D ratio, was used successfully in the 1800’s to treat rickets, a childhood disorder of bone development caused by Vitamin D deficiency.
In my opinion, a normal intake of Vitamin A from cod liver oil or other sources within the RDA should not be of concern, especially if properly balanced with Vitamin D through sunlight exposure or supplements. In special cases much higher doses of Vitamin A can be greatly beneficial, but these doses should be taken only under the supervision of a trained professional, and this study clearly points out some of the risks of not doing so.
