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Are you confused about vitamin A? Long before I knew anything about natural medicine, I had heard how dangerous this vitamin could be in excessive doses, especially for pregnant women.
I’m sure many of you have heard all the same things I did. And even more confusion still lingers from a widely reported 2002 study, which showed that a high intake of vitamin A increases the risk of hip fractures in postmenopausal women.
But now a new study has concluded that we don’t absorb vitamin A as efficiently as previously thought, so we should actually increase our dietary sources of the vitamin.
What to do? A closer look at both of these studies will weed out the facts from the myths.
The basics
Vitamin A is essential to the health of your eyes, bones, skin and immune system. Growth and healing also benefit from the antioxidants that this key vitamin supplies. And some studies have even shown that vitamin A may help fight cancer. So can you really get too much? The answer to that is Yes if you’re getting the wrong kind.
Researchers at the Harvard Medical School collected diet and supplement data from the Nurses’ Health Study for more than 72,000 postmenopausal women, aged 34-77. Over a period of 18 years their dietary questionnaires were updated periodically.
Analysis of the data revealed that subjects who consumed the most vitamin A from food sources had a 69% higher risk of hip fracture compared to women who consumed the least vitamin A. Women who had a high intake of dietary vitamin A and vitamin A supplements had an 89% higher risk of hip fracture.
Or those are the basic details that the mainstream media reported anyway. The actual conclusions of the Harvard study are not quite so cut and dried. But they do provide some useful guidance in determining the best way to get your vitamin A.
What’s in a name?
Vitamin A from food sources comes in two different forms: retinol and beta-carotene. Retinol is a vitamin A compound that has previously been associated with hip fractures in postmenopausal women. In comparison, beta-carotene (which the body converts into vitamin A) has not been associated with fracture risk.
Retinol can be found in a wide variety of animal foods, including: dairy products such as whole milk and whole milk yogurt, butter and cheese. Beef and chicken liver also contain retinol. And these are the foods that the Harvard research found to be associated with increased hip fracture risk. (An earlier study that used data from the same Nurses’ Health Study concluded that women who drank two or more glasses of milk per day increased their risk of fractures compared with women who drank less than one glass per week.)
The Harvard study also shows that most of the vitamin A supplements taken by the women in the study were included in multivitamins that contained a synthetic form of vitamin A – a form that delivered (yep, you guessed it) retinol. This vitamin A form has been associated with insufficient bone density and osteoporosis risk.
The preferable type of vitamin A is pro-vitamin A, also known as beta-carotene, and is abundant in dark green leafy vegetables and colorful orange vegetables and fruits (for which it helps supply the color) such as pumpkins, squash, sweet potatoes, peaches, apricots, cantaloupes, mangoes and (most famously) carrots.
In supplement form, beta-carotene is naturally available in fish oil. A particularly good source is cod liver oil, which contains beta-carotene along with vitamin D, and the combination of the two may provide excellent support for good bone health.
Up the intake
The most recent vitamin A study comes from researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University.
In two separate phases, the Tufts team fed 100 grams of pureed carrots and 300 grams of pureed spinach to male subjects. Analysis of serum blood samples revealed that, in both cases, considerably less absorption of beta-carotene took place than was previously thought.
Further studies will be needed to confirm that foods with high beta-carotene content need to be eaten in greater quantities to ensure adequate vitamin A intake. But let’s face it; a higher consumption of vegetables would do almost all of us a world of good. Nevertheless, the question lingers: Can you get too much vitamin A, even if it’s in the “right” form?
Apparently you can if you smoke cigarettes. Studies show that smokers with a high intake of beta-carotene are at greater risk of developing lung cancer. And, again, as the Harvard study demonstrates, postmenopausal women should avoid excessive intake of food sources and supplements that contain vitamin A in the retinol form.
As for just about everyone else, it’s almost impossible to overdo vitamin A consumption, according to HSI Panelist Allan Spreen, M.D. In fact, Dr. Spreen tells me there are only about two-dozen recorded cases of people who took too much vitamin A and suffered any distress whatsoever. Regarding supplement dosage, Dr. Spreen suggests that 10,000 IU of beta-carotene vitamin A per day is adequate.
If you still have questions or doubts about getting too much vitamin A, consult with your doctor or a dependable nutritionist to devise a balanced plan that’s right for you.
To Your Good Health,
Jenny Thompson
Health Sciences Institute
Sources:
“Vitamin A Intake and Hip Fractures Among Postmenopausal Women” Journal of the American Medical Association, Vol. 287, No. 1, 2002, jama.ama-assn.org
“Vitamin A Value of Spinach and Carrots as Assessed Using a Stable Isotope Reference Method in Adults” Experimental Biology 2004, Abstract #6305, select.biosis.org
“People Need to Eat More Beta Carotene to Get Enough Vitamin A” Research news from Tufts University, Friedman School of Nutrition Science and Policy: May 2004, eurekalert.org
“Beta-Carotene Levels May Be Too Low For Adequate Vitamin A” NutraIngredients.com, 4/27/04, nutraingredients.com
