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abstract & commentary
Synopsis: Vitamin D levels were low in 21% of black elderly subjects and 11% of white elderly subjects during the winter in Boston. None of the subjects who reported daily use of a supplement containing vitamin D had low levels.
Source: Harris SS, et al. J Clin Endocrinol Metab 2000;85:4125-4130.
Adequate vitamin d levels are critical for bone health. The skin makes vitamin D when it is exposed to adequate ultraviolet light. The elderly are at greatest risk for vitamin D deficiency because of their reduced exposure to sunlight and an age-related reduction in the skin’s synthetic capability. All populations living in northern latitudes are at risk for inadequate skin synthesis of vitamin D during the winter months because the appropriate wavelength of sunlight is not available during those months (roughly October through April inclusive). This study was undertaken to determine the extent of vitamin D deficiency in an inner city population in Boston in the winter. Harris and colleagues identified the 702 men and women born before 1935 (therefore at least 64 years old at the time of the study) who lived in any of the 14 subsidized housing units operated by the Boston Housing Authority and went to each site. Subjects completed standardized inventories and gave blood samples in February or March 1999. A total of 349 of the eligible subjects participated. About half of the subjects consumed less than one glass of milk daily and reported milk consumption did not differ by race. Fifteen percent of black men and 46% of white women reported regular daily use of vitamin D supplements, predominantly multivitamins. The best measure of vitamin D status is a serum 25-hydroxyvitamin D (25OHD). Serum levels were generally concordant with reported intakes. Serum calcium and parathyroid hormone levels were inversely correlated with serum 25OHD. Twenty-one percent of blacks and 11% of whites had 25OHD levels below 25 nmol/L. Currently there is no consensus as to what level is inadequate, but none of the subjects who took supplements containing vitamin D had 25OHD concentrations below 25 nmol/L. Optimal levels also have not been defined, but levels above 50 nmol/L are associated with suppression of parathyroid hormone and reduced risk of bone fracture. Harris et al note that mean wintertime vitamin D concentrations in white subjects in this cohort were about the same as in a cohort from the relatively affluent Boston suburb of Framingham and members of an HMO in Michigan. Harris et al also found that levels were consistently lower in smokers.
COMMENT by Sarah L. Berga, MD
Vitamin D is a steroid hormone that plays an important role in bone mineralization. In addition to its direct effects on bone, it increases calcium absorption from the gastrointestinal tract. A deficiency of vitamin D is a risk factor for osteoporosis and osteomalacia. More limited evidence links vitamin D deficiency with increased risk of hypertension, cardiovascular disease, diabetes, and some cancers. Vitamin D deficiency can be readily reversed by consuming foods fortified with vitamin D, by taking daily vitamin supplements, or by daily exposure to the appropriate wavelengths of sunlight. There are no foods that naturally contain vitamin D, however, many foods are fortified. Each eight-ounce glass of milk contains roughly 100 IU of vitamin D and most multivitamin preparations contain 400 IU. The recommended daily allowance has been set at 200 IU per day, but up to 800 IU is safe in adults. Not all diary foods are fortified with vitamin D, so it pays to read the label if one is attempting to get one’s daily requirements from food alone and does not intend to drink milk. Recently, some yogurt makers have been adding in vitamin D. However, many calcium-fortified beverages such as orange juice do not contain vitamin D. Consumers need to be aware that bone health is more than just a matter of calcium intake. Vitamin D and other minerals such as magnesium and phosphorus are also critical. The "bone health" story has been reduced to a "soundbite" about calcium, but doing so has led to an oversimplification that is misleading.
I recommend that all patients take a "general purpose" multivitamin daily. It need not be expensive or contain "fancy" ingredients. The two factors most difficult to obtain from food alone are vitamin D and folate. Both are critical to preventing many of the common diseases of aging. Both are contained in a general-purpose multivitamin.