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by Anna Lea Matysek

April 1, 2007

Vitamin D Deficiency

By Anna Lea Roof

Vitamin D is known as the “sunshine vitamin.”  The skin, when exposed to sunlight, manufactures copious quantities of Vitamin D.  So how could an active swimmer develop a Vitamin D deficiency?

It seems unlikely, but it happened to me. 

Vitamin D Basics

Calcium is required to build and maintain strong bones.  What many people do not know is that without an adequate supply of Vitamin D, the body cannot adequately absorb calcium.  Without Vitamin D, bones can become thin, brittle, or misshapen.  This condition in children is called rickets.

Vitamins are either fat-soluble or water-soluble.  Vitamin C, for example, is a water-soluble vitamin.  That means that it is not stored in the body; any unused excess is excreted by the body on a daily basis.  Vitamin D is a fat-soluble vitamin.  That means that it is stored in the body and used as it is needed.  It also means that if the body becomes deficient, it takes a long time (and a lot of Vitamin D), to get the levels back into the normal range. 

Vitamin D researchers are now finding that Vitamin D plays an important role in more than just bone health.  Evidence suggests that Vitamin D may be protective against several types of cancers.  Some Multiple Sclerosis researchers have hypothesized that low levels of Vitamin D may play a role in the development of MS.

The current recommended daily allowance (RDA) of Vitamin D for most adults is 400 IU (International Units) a day.  But Vitamin D does not occur naturally in very many foods.  Because rickets was a major health problem in the U.S. in the early 20th century, a milk fortification program was begun.  A glass of fortified milk contains about 100 IU of Vitamin D.

Leading Vitamin D researchers are convinced that the current RDA is much too low.  Most of them now think that 1,000 IU to 4,000 IU per day may be required to maintain adequate Vitamin D levels in the body.

The human body can manufacture its own Vitamin D when the skin is exposed to sunlight.  But a couple of conditions must be met.  The exposure has to be midday sun (10am to 3pm), on unprotected skin (no sunscreen).  And at our latitude, our skin can only manufacture Vitamin D from sunlight from May to September. 

According to Dr. Michael Holick, MD, of the Boston University School of Medicine, about 10 minutes of midday sun exposure over a large portion of the body, several times a week, is all that is needed to maintain adequate Vitamin D levels.  Dr. Holick’s views have met with criticism, however, from dermatologists who argue against any unprotected sun exposure due to the risk of skin cancer.  Dr. Holick does not advocate excess tanning; he recommends that sunscreen be applied after 10 minutes of unprotected exposure.  He cautions that one should NEVER get enough sun exposure to burn. 

The Deficiency

So, back to me.  In the summer, I swim outdoors.  By the end of the summer I have tan lines that persist through much of the winter.  How could I be deficient in Vitamin D?  I think it’s probably because of a combination of the factors mentioned earlier.  I swim outdoors, but during the week it’s late in the day (6:30pm).  That’s much too late to produce any Vitamin D from sunlight.  On Saturdays, we swim from 10:30am to noon.  But I always wear sunscreen for that workout; I would definitely get sunburned after 90 minutes of exposure.  And even though I take a daily multivitamin that contains 400 IU of Vitamin D, and drink a couple of glasses of milk each day, in my case the researchers must be right.  It obviously wasn’t enough. 

My doctor put me on prescription-levels of Vitamin D (50,000 IU a week) for five months.  At the end of that time, my level was back into the normal range.  I now take a maintenance dose of 2,000 IU a day.

The Results

At the time of my diagnosis, I felt fine.  I read all I could find on the Internet about Vitamin D deficiencies.  I didn’t find much about how it feels to be deficient in Vitamin D.  Besides the possibility of low bone density, most of the descriptions mentioned only vague symptoms such as “muscle fatigue.”

About four months after my diagnosis, I was at swim practice one night.  Our coach, Derek, said, “OK, that’s it.  You’re done.”  I looked at the clock in surprise.  I still had a lot of energy left.  It didn’t feel like I’d just swum a 90-minute workout. 

A few days later, the same thing happened.  As I drove home from the pool I wondered why I felt so energetic.  I hadn’t altered my sleep schedule, eating habits, or anything like that.  Finally I realized that I had been on the Vitamin D for four months.  My levels were probably nearing normal.    

As I thought back, I realized that I had been experiencing unusual fatigue in swim workouts for a long time - more than a year.  It was easy to blame a variety of factors: not enough sleep, job stress, aging.  I could remember workouts during the prior winter, wondering why I felt so tired while my 60-year-old lane mate (15 years my senior) seemed to be doing just fine.


Today, more than a year later, I feel even better.  My swimming stamina has continued to improve.  My times haven’t gotten any faster, but I guess I can’t have everything!