Get More Vitamin D

Summarized by Robert W. Griffith, MD
May 17, 2007

Summary

For years, the recommended daily allowance for vitamin D (400 IU daily) has been set too low; it was selected with the aim of preventing rickets, but now it's generally recognized that lowering the risk of osteoporotic fractures demands higher blood levels of the vitamin, with intake approaching 2,000 IU daily or more.

Introduction

Rickets is a disease of the past in almost all developed countries. Vitamin D deficiency is the main cause of rickets, but lack of dietary calcium can also be responsible. Children with this bone-softening condition are commonly found in developing countries where malnutrition and starvation are serious problems. In adults, the disease is called osteomalacia (literally, bone-softening).

Recommendations for minimal vitamin D intake were established in response to the risk of deficiency expressed as rickets or osteomalacia. While synthesized vitamin D became used to prevent rickets in the 1930s, it was not until the 1940s that a recommended daily intake was suggested: 10 µg (400 IU) of vitamin D was chosen because it approximated the amount found in a teaspoonful of cod-liver oil, which was an effective prophylaxis for rickets or osteomalacia.

In recent decades it's become clear that many adults in developed countries are not getting enough vitamin D to protect them from the risk of increased fractures as they get older. Fifteen eminent physicians from 8 different countries have written an editorial in the American Journal of Clinical Nutrition urgently promoting the need for widespread higher vitamin D intake.

Vitamin D blood levels

British researchers have estimated the prevalence of low vitamin D levels in a group of 45-year-olds.¹ They measured blood levels of 25-hydroxyvitamin D, which is the biologically active breakdown product of vitamin D. An 'acceptable' blood level that is not associated with disease is recognized as 72 nmol/L. In the British subjects, 87% had levels below 75 nmol/L, and about half of them had levels below 40 nmol/L; and 16% had levels below 25 nmol/L. These results were obtained in the winter and the spring, when vitamin D levels are lowest. In the summer and fall the percentages of inadequate subjects were considerably lower. 25-hydroxyvitamin D levels were higher in men during the summer and fall, and also in those taking vitamin D supplements or who ate oily fish. Obese people were more likely to have lower levels, as were Scottish participants. The researchers conclude that 'hypovitaminosis D' is alarmingly high during winter and spring in the general UK population, warranting 'action at a population level'.

A matter of dosage

Randomized clinical studies have shown that the recommended daily intake of 400 IU does not decrease the risk of fractures, whereas 700-800 IU daily does. The reduction in fracture frequency occurs when the blood level of 25-hydroxyvitamin D exceeds 72 nmol/L. Such levels are not likely to be achieved by normal nutrition. The exposure of skin to ultraviolet B light (obviously more in the summer and fall) is paramount, and this, together with supplements, may be the best way to ensure adequate vitamin D levels.

Supplements of 400 IU a day only raise the 25-dydroxyvitamin D by 7 to 12 nmol/L. To raise the level from 50 to 80 nmol/L one would require about 1,700 IU vitamin D supplementation daily. The US Food and Nutrition Board has estimated that the safe upper limit for vitamin D supplementation should be 10,000 IU daily, so that there's a pretty wide safety margin for supplement takers.

An alternative approach (or a complimentary one) would be to increase the fortification of foods. However, this requires an initiative from food manufacturers, development of appropriate foods, and regulatory approval, before it could make any impact.

Further possible benefits of raising intake

1. Two recent studies concluded that increasing the daily intake of vitamin D to 2,000 International Units could halve the risk of developing breast and colorectal cancer.

2. Lower 25-hydroxyvitamin D is associated with higher levels of HbA1c, a measure of long-term glucose concentration, so that generous supplementation might even help reduce the type 2 diabetic epidemic.

3. US nursing home residents with a high vitamin D intake have fewer falls, according to a new study.² Their average age was 89. Groups of 25 residents were randomly assigned to take 200 IU, 400 IU, 600 IU, or 800 IU of vitamin D, or placebo, for 5 months. Those taking the 800 IU level had a significantly lower rate of falling (72% lower, in fact) than those taking the placebo. Note that the number of falls was counted, not the number of fractures. How vitamin D reduces the number of falls is not clear.

Conclusions

There seems to be no disagreement among experts that higher intake of vitamin D is an urgent health measure that needs implementing for several populations in the USA and elsewhere - the young, the elderly, and those living in areas with low sun exposure. The 15 co-authors of the editorial urge new initiatives to change existing perceptions about daily values for vitamin D. Individuals can talk with their physician, and get advice concerning their need to take a supplement; in many cases, such a step will be necessary.

Source

• The urgent need to recommend an intake of vitamin D that is effective. Editorial. R. Vieth, H. Bischoff-Ferrari, B. Boucher,  et al. , Am J Clin Nutr, 2007, vol. 85, pp. 649--650

Footnotes
1. Hypovitaminosis D in British adults at age 45 y; nationwide cohort study of dietary and lifestyle predictors. E. Hypponen, C.  Power, Am J Clin med, 2007, vol. 85, pp. 860--868
2. A higher dose of vitamin D reduces the risk of falls in nursing home residents: a randomized, multiple-dose study. KE. Broe, TC. Chen, J. Weinberg,  et al., J Am Geriatrics Soc, 2007, vol. 55, pp. 234--239

Related Links
Vitamin D Strengthens Muscles and Prevents Falls
Don't Miss Out on Vitamin D
Are Older Folk at Risk of Vitamin D Deficiency?

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.