Tuesday, August 12, 2008

Vitamin D in the Spotlight

Vitamin D supplementation (finish the sentence correctly)

a. is usually not necessary as it is found in most foods
b. causes rickets, a bone disease
c. may protect against cancer
d. all of the above
e. none of the above.

The correct answer is C. Vitamin D has has received much attention recently. Several studies have reported an array of health benefits associated with vitamin D in children and in adults, possibly protecting against cardiovascular disease, certain cancers, and immune system disorders such as rheumatoid arthritis. These data have generated debate over the daily amount of vitamin D that should be recommended.

The current recommendation is 200 to 600 international units (IU) daily, depending on age. New data has emerged to question this guideline. There are very few food sources of vitamin D, namely fatty fish and eggs. Most of our vitamin D is synthesized in our skin through a process that requires sunlight. However, due to more sedentary lifestyles such as long working hours, web surfing, and playing video games, and heeding advice to avoid the sun to prevent skin cancer the level of vitamin D may be lower than our body requires. Some even suggest a worldwide pandemic of vitamin D deficiency.

It is well established that vitamin D deficiency causes rickets, a bone disease which usually affects children, in which the bones become very soft. See Dr. Janesta Noland's post on this blog regarding new vitamin D recommendations for children.

Additional benefits have been suggested for adults. In one study, vitamin D supplementation of 800 IU daily was associated with a decreased risk of colon cancer. This was shown to occur as a result of the expression of Bax - a protein that promotes the killing of damaged cells. In three meta-analysis observational studies, a serum 25-hydroxyvitamin D level of 30 ng/ml (75 nmol/L) or higher was associated with at least a 50% lower risk of breast cancer. As a result it has been suggested that women should be checked annually for vitamin D level to better identify their risk of breast cancer. A study funded by the National Institute of Health showed that women who took 1100 IU per day of vitamin D for 4 years reduced their risk of breast cancer by 60 percent.

Bottom line is that although it is not yet an official recommendation, based on recent studies, there may be a benefit to taking between 1000-2000 IU per day of vitamin D.

References: see above links. Am. J. Clinical Nutrition, 2007; 85:1586-91


Shannon said...

What are the best VEGAN sources for Vitamin D? I've read that vitamin D2 (ergocalciferol) isn't as effective as D3 (cholecalciferol), so what's the alternative if/when sunlight is insufficient?

Anne said...

Should I subtract out the Vitamin D that is in fortified milk products? Or is this recommendation above and beyond what you get in your diet? And roughly how much is there in an egg?

Dr. Taraneh Razavi said...

Hi Shannon

Although it is true that D3 is normally thought to be the more potent form of the vitamin, a recent study from Boston University (published in Journal of Clinical Endocrinology and Metabolism, Dec 2007)concluded that D2 and D3 are equally effective in raising the 25-hydroxyvitamin D level. This is good news since I don't know of any other sources of D3 than those that are derived from animal products.

Dr. Taraneh Razavi said...

Anne, the amount of vitamin D that is in an egg (the yolk really) is 20 IU per serving. The recommendation is for the total amount that you get in your diet so you don't need to subtract anything out. By comparison vitamin D fortified milk has about 100 IU per serving, salmon (3.5 oz) about 350 IU and cod liver oil (1 Tablespoon) about 1350 IU.

Shannon said...

ok another question I have is tangentially related, pertaining to sun exposure and the use of sun creams.

Personally, I've always felt that my best protection was in gradually developing my own defences. In spring, when my skin is at it's whitest (I'm English and blonde) I use a fairly high factor sun cream, but as the season progresses I decrease that to the point where last week I was out all day whitewater rafting and although my arms got a bit crispy, after some aloe they didn't even peel, they just faded into a darker tan. My theory is that my natural melanin is better for me than a bunch of chemicals. I'm over 40, don't have a single wrinkle, and have never had a hint of skin cancer. I think I'm doing wonders for my vitamin D production, and that a lot of skin cancer fears are manufactured by Ban du Solei... What do you think?

Dr. Taraneh Razavi said...

Shannon, it's a common belief that tanning protects the skin, but actually any tanning damages the skin. In general but not exclusively slow tanning is associated with certain types of skin cancer and the burn types are associated more with melanoma (the most serious type of skin cancer).
I think it is a good idea to continue to use the high factor screening year round.

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