Vitamin A and Osteoporosis, Summer Hours

• Letter to Our Readers

• Vitamin A Update

• The Harvard Nurses Study

• • What About Moderate Vitamin A Intake? - Two Studies Compared
  • The Role of Vitamin D
  • The Benefits of Vitamin A
  • Beta-carotene and other carotenoids
  • Dr. Rienstra's Advice

• Monroe Street Clinic News

Letter to Our Readers

We are delighted to be receiving your questions and comments in response to our monthly medical email newsletter. Your letters and emails let us know how we can best make "Medicine for People" useful and relevant to your lives. This month, we're giving the entire newsletter over to answering one of those queries, drawing on both the latest research and knowledge gained by treating patients in Dr. Rienstra's practice. In our answer we try to respect the complexity of the question. We know that some of you will enjoy learning the physiology of how nutrients affect our health or taking a closer look at the studies that make headlines. However, if you just want the bottom line, you can skip to specific recommendations which come at the end of the article. Whichever way you read it, we hope you find the information useful.

This month as always, we invite you to send your questions to Doctor Rienstra at MedicineForPeople@RienstraClinic.com.

Vitamin A Controversy Update

Dear Doctor,

Thanks, Douwe, for your newsletter. I find it informative and helpful. Sometimes you have a Q&A section. I wonder if you will address the controversy over vitamin A and bone loss. Is this something women should pay attention to? What are the benefits of vitamin A supplements compared with the risk of bone loss?

Peg

Dear Peg,

We did address this question in our July, 2002 newsletter. Here's an update of the topic.

Harvard Nurses Study

About a year ago the Harvard Nurses Health Study found that large quantities of Vitamin A, over 9000 IU daily, are associated with increased bone fractures in menopausal women. This seemed to be bad news for people taking larger doses for therapeutic reasons. Let's look at the details, however, and see what the real story is.

The Method

The study divided 72,337 women who had passed menopause into five groups of about 14,000 women each. One group, called the "first quintile" (quintile meaning "fifth") was that group which consumed the least vitamin A. The second group of about 14,000 women consumed slightly more vitamin A, and so on up to the fifth quintile which was that group which consumed the most vitamin A, in this case 9000 units a day and up.

How Strong was the Effect of Excessive Vitamin A?

In 18 years of observation of these 72,000 women, they suffered 603 hip fractures that were not due to severe trauma. (That means if a woman was in an auto accident and broke her hip, they did not count that as a fracture possibly related to vitamin A intake.) During that 18 years, the group of women getting the least amount of vitamin A suffered 85 fractures; that fifth of the women taking the most vitamin A suffered 125 fractures.

The Conclusions

Boiling those numbers down, for each thousand women in the high vitamin A group, over the eighteen year period, there were three extra women who suffered a fracture. The headline writers come up with "Excessive vitamin A causes hip fractures" because no one will read a headline that says "Excessive vitamin A taken over a period of eighteen years gives you three chances in a thousand of suffering a hip fracture."

The Shortcomings of the Study

No study is perfect, and one fault with the Harvard Nurses Study is that vitamin A intakes were estimated by five questionnaires the women completed over the eighteen years. Better would have been to check vitamin A levels in the blood. Given the expense of doing all those blood tests over the years, and the reality of getting the study done, the researchers did what they could and I consider this a minor quibble.

A more major quibble is that the top fifth of women, those who suffered more fractures, consumed 9000 units of vitamin A a day OR MORE. How much more is not noted, but if there were a thousand women in that group who consumed, say, 25,000 units or more of vitamin A, and all or most of the excess fractures were among those women, then the study's conclusion -- that more than 10,000 units a day is too much -- is unjustified.

What About Moderate Doses of Vitamin A? -- Two Studies Compared

Let's compare the Harvard Nurses Health Study with another, the Swedish Men's Study. Again, we'll look at people divided into five groups, or quintiles, based upon their answers to questionnaires about vitamin A intake. We will use the numbers the researchers obtained by adjusting the fracture count to correct for other risk factors such as smoking, weight, estrogen use, exercise, and drugs that affect bone strength.

In the Harvard Nurses Health Study, the fracture rate per thousand persons per 18 years was

• 1st quintile 8.2
• 2nd quintile 7.1
• 3rd quintile 8.4
• 4th quintile 8.6
• 5th quintile 9.5

First quintile has the lowest vitamin A intake and has 8.2 fractures per thousand women during the eighteeen year period. The women in the second quintile (who had slighter higher vitamin A intakes) had fewer fractures. Those taking an average or above-average amount had more fractures, about two extra fractures per thousand women per eighteen years in those consuming the most.

In the Swedish Men's Study, the fracture rate per thousand persons per 30 years was

• 1st quintile 41.3
• 2nd quintile 31.6
• 3rd quintile 24.6
• 4th quintile 31.8
• 5th quintile 53.9

The Conclusions

The details differ in the Men's Study, but whether you are a nurse in the Harvard study or a male Swede, it appears you want to be closer to the middle quintile of vitamin A intake as far as fracture rate is concerned. I'll suggest some dose levels later, but first it's important to look at other nutrients that may affect the rate of bone fractures.

The Role of Vitamin D

There is more to bone fracture rate than vitamin A intake. Vitamin D intake is an even greater factor. Notice that the rate of fracture in Sweden was far greater than in the US study, even when you take into account the fact that the Swedish study counted fractures for 30 years instead of 18. Vitamin D deficiency is the third most common vitamin deficiency worldwide. And vitamin D, as you know, is important for bone strength. Vitamin D deficiency is much more common in northern climes such as Scandinavia, site of the Swedish studies on vitamin A and osteoporosis.

The Vitamin A/Vitamin D Connection

So what's the vitamin A/vitamin D connection? Some researchers believe higher doses of vitamin A can flood part of the system by which we utilize vitamin D, thus elbowing out this important vitamin. This may be true, but the jury is still out. While some studies support the conclusion that excessive vitamin A intake increases fracture rate, other studies showed no loss of bone density. The Journal of Bone Mineral Research reported in December, 2001 (vol 16, pages 2306-12) that "High serum retinyl esters (a form of vitamin A) are not associated with reduced bone mineral density in the Third National Health And Nutrition Examination Survey, 1988-1994." Similarly, the Journal of Clinical Epidemiology in 1990 (vol 43, pages 693-9) "observed no statistically significant relationship between vitamin A supplement use or serum retinol (another form of vitamin A) with radial bone mass or fractures." (the radius is a bone in your forearm).

Benefits of Vitamin A

If you really want to know the optimal intake of vitamin A, you need to look not just at fracture rate, but also at overall rates of illness and death compared to vitamin A intake. For example, on June 27, 1992 the Lancet reported that people with above average levels of vitamin A recovered more rapidly and more completely from stroke. They concluded, "Our results suggest a beneficial effect of a high serum vitamin A concentration on early outcome in ischaemic stroke."

Beta-carotene and other carotenoids

When you read your vitamin label, don't confuse vitamin A with beta-carotene, sometimes labeled as "vitamin A equivalent". Beta-carotene is a substance found in carrots and many other vegetables. Our metabolic processes can turn beta-carotene into Vitamin A. These metabolic processes, however, will turn off if there is adequate vitamin A on board. You can take all the beta-carotene you want and your body will not turn it into excess vitamin A and cause vitamin A poisoning.

Note that there are many other new "carotenoids" on the block, such as lutein, lycopene, and zeaxanthin, now known to be essential for good health of the eyes. Excess beta-carotene can interfere with the absorption of these other carotenoids. Studies in Scandinavia of antioxidants produced the unexpected result that male smokers died sooner when given beta-carotene. This is touted as evidence of the dangers of vitamins. I think those smokers died not from too much beta-carotene, but from a relative deficiency of the other carotenoids. In other words, the beta-carotene supplement crowded out other, important, carotenoids.

Pediatricians have all seen a condition of children called "carotenemia," caused by excess intake of carrots and other yellow vegetables, in which beta-carotene levels are so high that the skin turns a yellow-orange. But yellow skin is the only problem these kids have.

Dr. Rienstra's Advice

Taking all this together, I think 5000 to 7500 units of vitamin A daily is a reasonable and safe intake. I base this upon a synthesis of the available information and reserve the right to change my mind as more information becomes available. If you have dry skin, lots of sinus problems, fatty food intolerance, heavy calluses, or poor night vision, you may be deficient in vitamin A and require some individual attention.

It's true that vitamin A is a poison, in sudden doses of a one to five million units, depending on the individual. However, short-term doses of 100,000 units of vitamin A for a week or so can be very helpful to treat infections.

Pregnant women need to keep their vitamin A intake at 10,000 units or less per day, from both supplements and diet. But they also need to realize that vitamin A deficiency leads to birth defects as well. Third-world women are frequently low in vitamin A. One result is an increased rate of transmission of HIV to their babies.

In conclusion, eat whole foods, freshly prepared. Chose a supplement of mixed carotenoids if you do take one, and recognize that high doses of single nutrients can have unexpected effects.