ABSTRACT
INTRODUCTION: Previously we reported seasonal variation in 25-hydroxyvitamin D (25OHD) levels in postmenopausal women living in a subtropical climate. Because studies have suggested that there are gender differences in 25OHD levels, we sought to determine (1) the levels and determinants of 25OHD in men drawn from the same community, (2) whether seasonal variation of 25OHD occurs in men at this latitude (37 degrees S), and (3) whether these findings were comparable to those we previously observed in postmenopausal women. METHODS: Cross-sectional study of 378 healthy, middle-aged and older community-dwelling men in Auckland, New Zealand. RESULTS: The mean 25OHD (SD) level was 85 (31) nmol/l. We found significant seasonal variation in 25OHD levels (peak in autumn 103 nmol/l, nadir in spring 59 nmol/l). Vitamin D insufficiency (25OHD <50 nmol/l) was uncommon (prevalence in summer 0-17%, in winter 0-20%). The major determinants of 25OHD were month of blood sampling, fat percentage, physical activity, and serum albumin. Men had higher levels of 25OHD throughout the year than women did, a finding that persisted after adjusting for potential confounding factors. In men and women the determinants of 25OHD were similar. CONCLUSION: There is significant seasonal variation in 25OHD levels in men living in a subtropical climate. In contrast to postmenopausal women, men have low rates of suboptimal vitamin D status, even in winter. Routine vitamin D supplementation for this population of men is not warranted.
Subject(s)
Vitamin D/analogs & derivatives , Adipose Tissue/physiology , Adult , Aged , Aged, 80 and over , Body Weight/physiology , Climate , Cross-Sectional Studies , Dietary Supplements , Environmental Exposure , Exercise/physiology , Female , Humans , Male , Middle Aged , New Zealand/epidemiology , New Zealand/ethnology , Prevalence , Seasons , Ultraviolet Rays , Vitamin D/administration & dosage , Vitamin D/blood , Vitamin D Deficiency/epidemiology , Vitamin D Deficiency/ethnologyABSTRACT
PURPOSE: To assess the effect of the antiestrogenic agent tamoxifen on bone mineral density in normal late postmenopausal women. METHODS: A randomized, double-blind, placebo-controlled trial was performed with 57 healthy, late postmenopausal women (mean 11 +/- 7 years since menopause). Subjects were assigned to take either tamoxifen 20 mg/d or placebo for 2 years. Total body, lumbar spine, and proximal femoral (femoral neck, Ward's triangle, trochanter) bone mineral densities were measured every 6 months using dual-energy x-ray absorptiometry. Serum and urine indices of bone turnover were measured at baseline, 6 months, and 2 years. RESULTS: In the women given tamoxifen, the mean bone mineral density of the lumbar spine increased by 1.4%, while that in the women given placebo declined by 0.7% (P < 0.01 for difference between groups). Total body bone mineral density declined in both groups, but less so in the tamoxifen-treated women (P < 0.05). At both sites, the effect of tamoxifen was maximal after 1 year, with no further separation of the groups thereafter. There was no significant effect of tamoxifen on bone mineral density in the proximal femur. Tamoxifen produced significant falls in serum alkaline phosphatase (P < 0.0001), ionized calcium (P < 0.0001), and phosphate (P < 0.01), and in urinary excretion of hydroxyproline, n-telopeptides, and calcium (P < 0.05 for each). CONCLUSIONS: In normal late postmenopausal women, tamoxifen at a dose of 20 mg/d exerts a small protective effect on bone mineral density, comparable in magnitude to that of calcium supplementation and less than that of either estrogen or the bisphosphonates. Tamoxifen is unlikely to supersede any of these therapies in the management of postmenopausal osteoporosis.