Living ~400lbs

… and believe me I am still alive

Fat folks more likely to be Vitamin D-deficient?

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…

  1. 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.
  2. 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.
  3. 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.  :)


Vitamin D and Obesity

Are We Getting Enough Sun?

Healthlink: Vitamin D

Decreased bioavailability of Vitamin D in Obesity

The Vitamin D Epidemic and its Health Consequences

Seattlites Don’t Get Enough ‘Sunshine Vitamin’

2 responses to “Fat folks more likely to be Vitamin D-deficient?”

  1. this is from the Vitamin D Council’s website:

    What We Recommend

    If you use suntan parlors once a week or if you live in Florida and sunbathe once a week, year-round, do nothing. However, if you have little UVB exposure, my advice is as follows: healthy children under the age of 2 years should take 1,000 IU per day—over the age of 2, 2,000 IU per day. Well adults and adolescents between 80–130 pounds should start with 3,000 IU per day while those over 130 pounds but less than 170 pounds should take 4,000 IU per day. Those over 170 pounds should receive 5,000 IU per day. Two months later have a 25-hydroxy-vitamin D blood test, either through ZRT or your doctor.

  2. I too am fat and vitamin-D deficient—but my thyroid doctor made it sound as if that is connected to having a poorly functioning thyroid, because the parathyroids are what help to regulate that in the body (making more if you need it.) Since being hypothyroid is also connected to having a slower metabolism and a higher body weight, I wonder if that’s the reason for the connection?

    I’m in my mid-20s, 328 lbs, and live in Virginia, previously from Ohio . . . so there really isn’t any reason I shouldn’t be getting enough, haha.

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About Me

Former software tester, now retired heart patient having fun and working on building endurance and strength. See also About page.

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