Vitamin D insufficiency among free-living healthy young adults

Abstract

Long-term vitamin D insufficiency can cause secondary hyperparathyroidism and osteomalacia (1). In addition, there is increasing evidence that vitamin D may protect against common cancers, such as cancer of the colon (2-4), prostate (5), and breast (6). Young adults aged 17 to 35 years drink inadequate amounts of milk (7) and are concerned about exposure to the sun because of the fear of developing skin cancer (8,9), which increases the risk of vitamin D insufficiency (10). We sought to examine the prevalence of vitamin D insufficiency in a group of free-living healthy young adults, consisting of mostly health care professionals, in Boston, Massachusetts. SUBJECTS AND METHODSWe recruited hospital employees, attending physicians, house staff physicians, medical students, and hospital visitors during our vitamin D awareness screening program at Boston University Medical Center during March and April, 1999 (end of winter) and September and October 1999 (end of summer). Subjects were excluded if they had a history of intestinal malabsorption. Subjects were divided into four age groups: 18 to 29 years, 30 to 39 years, 40 to 49 years, and ≥50 years. Study participants gave written informed consent.A questionnaire was administered to assess the intake of foods and supplements containing vitamin D. Approximately 5 mL of blood was drawn for determination of 25-hydroxyvitamin D and intact parathyroid hormone levels. Analysis of 25-Hydroxyvitamin D and Parathyroid Hormone LevelsThe serum assay for 25-hydroxyvitamin D (D 2 and D 3 ) was performed according to the method of Chen et al. (11). The limit of detection was 5 ng/mL, and values below the limit of detection were assigned 5 ng/mL. The assay has an intra-assay coefficient of variation of 8% and an inter-assay coefficient of 12%. Parathyroid hormone level was determined using a chemiluminescence assay kit (Nichols Institute Diagnostics, San Juan Capistrano, California). This assay has both intra-and inter-assay coefficients of variation of 6%. Statistical AnalysisWe used the unpaired Student t test to compare mean 25-hydroxyvitamin D and intact parathyroid hormone levels between groups. Results are presented as means ± SD. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript squared tests were used to calculate differences in proportion of vitamin D insufficiency, which was defined as a 25-hydroxyvitamin D level ≤20 ng/mL (12). P values <0.05 were considered statistically significant. Microsoft Excel (Seattle, Washington) and Epi-Info (Atlanta, Georgia) programs were used for all statistical calculations. RESULTS Baseline CharacteristicsOne hundred sixty-five subjects were enrolled at the end of winter and 142 subjects were enrolled at the end of summer, of whom 61% were women (n = 186) and 60% were white (n = 185). Dietary HistoryMost subjects drank milk: 64% (n = 91) in the end-of-summer group and 58% (n = 96) in the end-of-winter group. An average of 1.6 ± 1.0 glasses of milk was drunk per day. There was no statistical difference betwee...

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