Wednesday, June 25, 2008

Optimal vitamin D doses

I thought everyone had heard the news about the widespread deficiencies in vitamin D, yet the majority of people whose D levels I check measure way, way low in this essential vitamin. Even those who take a daily multi-vitamin with 400 units of D per tablet (the current RDA) are failing to top 30 ng/ml, the lower end of the desirable range.

Doctors in Beirut studied two groups of adolescents over 16 weeks. Half took 1400 units of D3 per week (the RDA for this age group is 200 units) and the other half took 14000 units per week. By study's end, the high dose group had a significant upward change in their serum D levels, but, better yet, demonstrated "substantial increments in lean mass, bone area, and bone mass."(1)

Many of my patients take 400 units of D3 per day, the amount present in most multi-vitamin pills. Per Toronto's Dr. Reinhold Vieth and colleagues "Supplemental intake of 400 IU vitamin D/d has only a modest effect on blood concentrations of [vitamin D], raising them by 7–12 nmol/L [2.8-4.8 ng/ml], depending on the starting point."(2) So if you're skidding along in a pasty white fashion, no sun plus one multivitamin pill/day, and your vitamin D level is around 11 (like so many of my patients), adding one more 400 unit D tablet per day will only get you up to 15, still terribly deficient.

Experts recommend supplementation in the neighborhood of 2000 units per day. Studies suggest that fracture risk falls with D levels of 30 ng/ml, and the improved outcomes not only result from stronger bones but also from greater muscle strength.
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(1)Maalouf J, et al "Short term and long term safety of weekly high dose vitamin D3 supplementation in school children" J Clin Endocrinol Metab 2008; DOI: 10.1210/jc.2007-2530.

(2)Vieth, R et al. "The urgent need to recommend an intake of vitamin D that is effective" American Journal of Clinical Nutrition, Vol. 85, No. 3, 649-650, March 2007

8 comments:

Ruth said...

2000 mg is a lot of supplementation. Did we used to get that amount from the sun? I have stopped taking Vit E which was once recommended highly. I think people get confused by being told something is necessary and then finding out 20 years later it was bad for them.

kenju said...

I take 1000 units per day, and once I had to take RX strength. I noticed that my fingernails grew strongly and rapidly during that time - the only time in my life that they have.

Amy said...

So how do you know if you're getting enough Vit D naturally? I'm not worried now b/c I live in FL and am at the beach all the time, but I'm probably moving this summer and wondering if I should supplement when I do.

Reality Man said...

As your readers know, it's your brother here. Ruth is onto something: what is up with us/medical science at this late date in our evolution that we need to take so much of something that cannot be gotten out of foods? I, for the time being, am continuing to expose my dark, leathery, unwashed skin to the sun.

Reality Man said...

OK, I'll take my own shot at it. We used to be able to use up high energy cholesterol in multi-day long hunting, but MDLH and farming and other outdoor pursuits gave way to pencil pushing, form shuffling, consulting, and video game playing. Those who managed to survive that transformation still can benefit from what used to be supplied by being outside: exercise and Vitamin D.

Cilicious said...

Like Ruth, I used to supplement Vit E, then quit. Like Amy, I live in FL and do get sun, and like Reality Man, my weathered skin shows the effect. I had a bone scan which showed osteopenia.
I do some of the right things. I take a regular vitamin supplement.
I guess increasing my Vit D won't kill me--and might help. I've read about Vit K, too, but I suppose that is a whole other study which, at some point, I'll be reading about.

Femail doc said...

Ruth and Reality Man: These mega-doses have been devised to bring our sad little levels up to optimal; I should think once you're repleted, smaller doses will do. RM, you've got the scenario right; human genome was developed during Ice Age for best survival under conditions of cold, famine, and obligatory exercise. I guess I better add sunshine to that. One researcher theorized that little blond children were an evolutionary answer to humans living in less than sunny Northern climes, allowing them to get maximum D from minimal summer sun exposure at a time in their lives when D (for bone development) was most essential. Then little blond children grown up into ungrateful brunette teenagers.

Ruth and Cilicious: I've got some info on E and K; I'll put that in another post.

Amy: I'm sure you're rolling in D now. I'd keep up at least 400 units daily in a multivitamin, then maybe get your D levels checked in years to come. If I get more info on maintenance levels for D supplementation, I'll let you know.

KJ: Wish D would make my nails less brittle.

Mauigirl said...

My vitamin only has the 400 IU of D in it; I also drink milk twice a day. I wonder how much more I need. I do sit out in the sun on weekends and after work on our deck. I hope it helps!