Ask a Scientist -- Dr. William B. Grant, PhD
Questions and Answers with Dr. William B. Grant, PhD
Sunlight, Nutrition and Health Research Center
Response to newsletter, August 12, 2015
In this newsletter on vitamin D utilization we shared a story of one of our D*action participants - how regular testing of his D levels showed a dramatic drop after fighting an illness.
Vitamin D study concludes supplements won’t strengthen bones
Q: How do you counter conclusions reached in the study appearing in JAMA and this article?
A: The trial by Hansen et al (1) was poorly designed. They started with participants with an average baseline vitamin D level of 21 ng/mL and increased it to 27 ng/mL. According to Robert Heaney, they should have started with an understanding of the vitamin D level-health outcome relation, enrolled people with vitamin D levels near the low end of the relation, and given enough vitamin D to raise vitamin D levels to an upper region of the relation. The vitamin D level-bone mineral density relation for elderly women is given in Ref. 3. It is seen in that paper that there is about a 4% difference in bone mineral density for part of the hip for vitamin D levels above 40 ng/mL compared to 10 ng/mL. They would have been able to see that amount of change. In a recent paper, we found that vitamin D trials that enrolled people with vitamin D levels less than 20 ng/mL had a 50% chance of reducing biomarkers of inflammation but that trials starting with higher levels had a 25% chance (4).
Vitamin D synthesis rate
Q: I am Dr.Gonzalez,from Paraguay. I want to know Vitamin D rate of synthesis with sun exposure in elderly,60+years old.
A: Well, vitamin D synthesis depends on many factors including age, skin pigmentation, amount of skin surface area exposes, location, surface elevation, season, time of day, aerosol and cloud loading, etc. The open access paper by Endelsen gives some guidance on season and latitude. As to time of day, near to solar noon is best since the intensity of UVB, which produces vitamin D, is highest and the ratio of UVA to UVB is lowest; UVA, the long wave UV, is implicated as a risk factor for melanoma and non-melanoma skin cancer.
I have a vitamin D production meter from Solartech that gives the vitamin D production rate in IU/min for a young person with 10% of his/her body surface area exposed. Elderly people take as much as four times longer to produce vitamin D from UVB than younger people do.
The best way to determine how much time you need to spend in the sun to reach your vitamin D level goal is to set a pattern, say, 20 minutes in midday, with 10-20% of your body surface exposed, do it for a month or two, then have your vitamin D level measured. Of course the time would have to be adjusted as the seasons change, and the paper by Engelsen would be useful.
What to do with high levels of vitamin D
Q: Dear Dr. Grant, I checked my d-levels and it was 83. Now my nutritionist insists I stop taking 5000 IU daily. He wants me to take no more than 2000 IU daily. I would like your opinion on this.
A: Well, 83 ng/mL is relatively high. However, there is limited risk for this value. There are a number of papers in the journal literature reporting poorer health outcomes for people with vitamin D levels above 30 ng/mL. However, the reason for many of these papers seems to be that people were advised by their physician to take vitamin D because of vitamin D deficiency, such as evidenced by low bone mineral density and osteoporosis, and taking vitamin D for a short time cannot overcome the adverse effects of low vitamin D for many years. As reported in a recent paper (1), physicians are much more likely to prescribe vitamin D in the northern U.S. states than in the central or southern ones.
GrassrootsHealth recommends 40-60 ng/mL. This range is generally well supported by observational studies of vitamin D levels and health outcomes, and is the range for people spending lots of time in the sun.
There are, however, some physicians who recommend vitamin D levels above 60 ng/mL for their patients and report good outcomes. Unfortunately, most of these studies have not been published, so cannot be used as the basis for health policy.
There seems to be at least one adverse outcome of higher vitamin D levels for men: increased risk of prostate cancer(2). There do not seem to be similar adverse outcomes for women.