I got a phone call from my RNP; my screening tests show no problems, but my vitamin D is still a little low. She suggested I continue to take a 1000iu Vitamin D tablet a day. During my checkup RNP also urged me to start taking a multivitamin again. I have, and it has 400iu of vitamin D too. So now I’m actually getting 1400 iu of Vitamin D a day from pills, plus whatever’s in milk and fish.
I began to wonder if this was too much, so I started playing with Google…and found that being fat is correlated with increased risk of vitamin D deficiency.
- Producing from sunlight. One study compared how much vitamin D fat women produced from UVB rays vs “normal” weight women. Both groups increased their vitamin D levels, but the increase in vitamin D from the simulated sunlight was 57% lower in the fat women. (Chart – note “BMI” should be “Body weight (kg)”.) This implies that fat people need more sun exposure to produce the same amount of vitamin D.
- Absorbing from pills. The study also compared how much vitamin D was absorbed from oral supplements. Again, both the fat and thin women increased their vitamin D levels, but the thin women absorbed more. (Chart – note “BMI” should be “Body weight (kg)”). This implies that fat folks need higher oral doses of vitamin D.
Well, being fat may be one reason why my vitamin D levels are low. But there are others. For example…
- I live in Seattle This is not just a comment on our vaulted frequency of overcast days. The closer you get to the poles, the more oblique the angle of the sun gets during fall and winter, which reduces the amount of vitamin D produced from sun exposure.In addition, cloud cover, shade, pollution, and sunscreen all reduce vitamin D production.
- Aging As you get older, your skin has less of the precursers it needs to create vitamin D. Maybe when I was 20 I was producing enough, but not now.
- Skin Color Melanin is an extremely effective UVB sunscreen, and UVB is needed to produce vitamin D. The more pigment your skin has, the longer it will take to produce vitamin D.
So, yes, I’m taking supplements, and yes, it’s (still) below the recommended upper daily limit of 2000 iu. :)
Decreased bioavailability of Vitamin D in Obesity
The Vitamin D Epidemic and its Health Consequences
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