Susie is a petite 5 ft 3 inch woman who weighs 102 lbs. Her starting 25-hydroxy vitamin D level was 42 ng/ml in summer.
Claire, on the other hands, struggles with her weight. Also at 5 ft 3 inches but weighing 221 lbs, Claire's starting vitamin D level was 23 ng/ml, also during the summer - severe deficiency.
I ask patients to supplement with vitamin D at a dose sufficient to increase 25-hydroxy vitamin D levels to 60-70 ng/ml.
For Susie, this required 1000 units. Her blood level: 67 ng/ml.
For Claire, this required 8000 units - an 800% higher dose.
Weight, specifically fat weight, exerts a dramatic effect on our vitamin D requirements. Some of the greatest vitamin D needs I have seen are in overweight people.
This effect of weight on vitamin D need has been demonstrated in:
- Children and adolescents
- Elderly (over age 65 years)
- Men and women
In other words, the weight phenomenon seems to be shared regardless of race, sex, or age. The bigger you are, the more fat you have, the greater your vitamin D need. Why? It's not entirely clear whether vitamin D is stored in fatty tissue, or whether obesity somehow interferes with vitamin D metabolism. Though a much smaller contributor, heavier people also, on average, tend to spend less time outside and show less skin surface area for vitamin D activation.
How about people who lose weight? Let me tell you about another patient, Penny.
At the start, Penny's 25-hydroxy vitamin D blood level showed the usual deficiency at 22 ng/ml. She supplemented with 8000 units of vitamin D. Several months later, another 25-hydroxy vitamin D blood level showed a level of 67.8 ng/ml, right on target.
Penny also began a diet (the diet that I advocate which includes elimination of wheat, cornstarch, and sugars) and, over 6 months, lost 34 lbs. Now a much trimmer 146 lbs, another vitamin D blood level: 111 ng/ml - too high.
I therefore instructed Penny to reduce her vitamin D dose to 4000 units per day, a much reduced dose due to her wonderful weight loss.
So it is important to remain aware of the weight-sensitive phenomenon with vitamin D. The heavier you are, in general, the more vitamin D you need to achieve a healthy level; the thinner you are - or become - the less vitamin D you need.