Susan S. Harris

Effect of Calcium and Vitamin D Supplementation on Bone Density in Men and Women 65 Years of Age or Older

BACKGROUND Inadequate dietary intake of calcium and vitamin D may contribute to the high prevalence of osteoporosis among older persons. METHODS We studied the effects of three years of dietary supplementation with calcium and vitamin D on bone mineral density, biochemical measures of bone metabolism, and the incidence of nonvertebral fractures in 176 men and 213 women 65 years of age or older who were living at home. They received either 500 mg of calcium plus 700 IU of vitamin D3 (cholecalciferol) per day or placebo. Bone mineral density was measured by dual-energy x-ray absorptiometry, blood and urine were analyzed every six months, and cases of nonvertebral fracture were ascertained by means of interviews and verified with use of hospital records. RESULTS The mean (+/-SD) changes in bone mineral density in the calcium-vitamin D and placebo groups were as follows: femoral neck, +0.50+/-4.80 and -0.70+/-5.03 percent, respectively (P=0.02); spine,+2.12+/-4.06 and +1.22+/-4.25 percent (P=0.04); and total body, +0.06+/-1.83 and -1.09+/-1.71 percent (P<0.001). The difference between the calcium-vitamin D and placebo groups was significant at all skeletal sites after one year, but it was significant only for total-body bone mineral density in the second and third years. Of 37 subjects who had nonvertebral fractures, 26 were in the placebo group and 11 were in the calcium-vitamin D group (P=0.02). CONCLUSIONS In men and women 65 years of age or older who are living in the community, dietary supplementation with calcium and vitamin D moderately reduced bone loss measured in the femoral neck, spine, and total body over the three-year study period and reduced the incidence of nonvertebral fractures.

Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women.

OBJECTIVES To determine whether relative vitamin D deficiency during the winter months contributes to age-related bone loss and whether rates of change in hard- and soft-tissue mass vary during the year. DESIGN Double-blind, placebo-controlled, 1-year trial in 249 women in which equal numbers of women were randomized to either placebo or 400 IU of vitamin D daily. All women received 377 mg/d of supplemental calcium largely as calcium citrate malate. PATIENTS Healthy, ambulatory postmenopausal women with usual intakes of vitamin D of 100 IU/d. MEASUREMENTS Duplicate spine and whole-body scans were done by dual energy x-ray absorptiometry at 6-month intervals that were timed to periods when 25-hydroxyvitamin D levels were highest and lowest. Period 1 was June-July to December-January and period 2 was December-January to the next June-July. Serum parathyroid hormone and plasma 25-hydroxyvitamin D levels were measured during periods 1 and 2. MAIN RESULTS In the placebo group, spinal bone mineral density increased in period 1, decreased in period 2, and sustained no net change. Women treated with vitamin D had a similar spinal increase in period 1 (1.46% compared with 1.40% in placebo), less loss in period 2 (-0.54% compared with -1.22%, CI for the difference, 0.05% to 1.31%, P = 0.032) and a significant overall benefit (0.85% compared with 0.15%, CI for the difference, 0.03% to 1.37%, P = 0.04). In period 2, 25-hydroxyvitamin D levels were lower and parathyroid hormone levels were higher in the placebo than in the vitamin D group. Whole-body lean and fat tissue and bone mineral density varied during the year but did not change overall. CONCLUSIONS At latitude 42 degrees, healthy postmenopausal women with vitamin D intakes of 100 IU daily can significantly reduce late wintertime bone loss and improve net bone density of the spine over one year by increasing their intake of vitamin D to 500 IU daily. A long-term benefit of preventing vitamin D insufficiency in the winter seems likely although it remains to be shown. Observed changes in bone as well as in fat and lean tissue appear to be related to season.

Association between serum osteocalcin and markers of metabolic phenotype.

CONTEXT Osteocalcin has been reported to contribute to the regulation of glucose tolerance and insulin secretion and sensitivity in experimental animals. OBJECTIVE Our objective was to examine the association between serum osteocalcin concentration and markers of dysmetabolic phenotype using data from a completed clinical trial in adults age 65 and older [n = 380, mean age 71 yr, body mass index (BMI) 26.9 kg/m(2), 5% with diabetes]. RESEARCH DESIGN AND METHODS In cross-sectional analyses (baseline data), we estimated the associations of serum osteocalcin and urine N-telopeptide with markers of metabolic phenotype including fasting plasma glucose (FPG) (primary outcome), fasting insulin, insulin sensitivity estimated by homeostasis model assessment for insulin resistance, plasma high-sensitivity C-reactive protein, IL-6, and measures of adiposity (BMI and body fat) (secondary outcomes) after multivariate adjustment for potential confounders. In prospective analysis (placebo arm), we estimated the associations of osteocalcin and N-telopeptide with change in the primary outcome, FPG, over a 3-yr period. RESULTS In cross-sectional analyses, serum osteocalcin concentration was inversely associated with FPG (P = 0.01), fasting insulin (P = 0.006), homeostasis model assessment for insulin resistance (P = 0.002), high-sensitivity C-reactive protein (P = 0.01), IL-6 (P = 0.02), BMI (P < 0.001), and body fat (P < 0.001). When participants were divided into tertiles by serum osteocalcin, mean FPG was 97.1 vs. 104.8 mg/dl in the highest vs. lowest osteocalcin tertile, respectively (P < 0.01). In prospective analyses, exposure to higher osteocalcin levels during follow-up was associated with a significantly lower rise in FPG at 3 yr. Urine N-telopeptide was not associated with any marker of metabolic phenotype. CONCLUSIONS Serum osteocalcin concentration was inversely associated with blood markers of dysmetabolic phenotype and measures of adiposity. Our findings should be considered hypothesis generating, and they need to be replicated in human studies designed to test the hypothesis that osteocalcin affects metabolism.

The vitamin D receptor start codon polymorphism (FokI) and bone mineral density in premenopausal American black and white women

This study examines the association between bone mineral density (BMD) and a start codon polymorphism (SCP) at the translation initiation site of the vitamin D receptor (VDR) gene. The thymine/cytosine (T/C) polymorphism in the first of two start (ATG) codons can be detected by a restriction fragment length polymorphism (RFLP) using the endonuclease FokI, which recognizes ATG as part of its restriction site. F indicates absence of the first ATG and a VDR that is shorter by three amino acids. The FokI genotype was determined in 154 premenopausal American women (72 black and 82 white) who were 20–40 years old. BMD of the total body, femoral neck, and lumbar spine were measured by dual‐energy X‐ray absorptiometry. The distribution of the SCP genotypes differed significantly by race (p < 0.001): 4% of blacks versus 18% of whites were ff homozygous and 65% of blacks versus 37% of whites were FF homozygous. There was no statistically significant interaction between race and SCP genotype in analyses of BMD at any skeletal site. In the group as a whole, the ff women had femoral neck BMD that was 7.4% lower than that of the FF women. The ff white women had total body BMD values that were 4.3% lower and femoral neck values that were 12.1% lower than FF white women. Total body and femoral neck BMD did not differ significantly by genotype in black women, and spine BMD did not differ by genotype in either race. Addition of the SCP genotype to analysis of covariance models comparing BMD of the black and white women reduced estimated differences in femoral neck BMD between the two groups by about 35%. In conclusion, the SCP polymorphism, detected with the endonuclease FokI, appears to influence peak bone density, particularly at the femoral neck. Racial differences in its distribution may explain some of the racial difference in femoral neck BMD.

Accelerated bone loss in hypothyroid patients overtreated with L-thyroxine

OBJECTIVE To compare the rate of bone mineral loss in thyroxine-treated women with low thyrotropin (thyroid stimulating hormone, TSH) levels with that in women without known thyroid disease. DESIGN Cases selected from a prospective calcium trial. SETTING Subjects were recruited from the Boston area. MEASUREMENTS AND MAIN RESULTS Of 361 women enrolled in a 2-year calcium supplement trial, 18 received thyroxine for hypothyroidism. Of these, 10 were considered overtreated, because they had low TSH levels. Rates of loss of bone mineral density from the radius, spine, and hip during 1.9 +/- 0.6 years were measured by single- and dual-photon absorptiometry. When compared with women with no known thyroid disease (236 controls for the spine, 246 for the radius, and 237 for the femoral neck), women with low TSH levels had greater annualized, adjusted mean rates of bone loss from the spine (-2.89% +/- 0.65% compared with -1.13% +/- 0.13%, P = 0.009) and similar but not significant trends at the radius (-1.18% +/- 0.75% compared with -0.13% +/- 0.17%) and femoral neck (-1.39% +/- 0.80% compared with -0.28% +/- 0.19%). These means were adjusted for variables that affected the rate of loss in the control group (baseline bone mineral density and body mass index, calcium intake, and years since menopause). There were no statistical differences between the low TSH and control groups for any laboratory variables measured, including serum calcium, phosphorus, parathyroid hormone or alkaline phosphatase, plasma 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D, or 24-hour urine calcium-to-creatinine ratio. CONCLUSIONS Thyroxine-treated women with low TSH levels lose bone mineral from the spine more rapidly than do women without known thyroid disease. These patients are therefore at increased risk for osteoporosis. The absence of detectable biochemical changes in women with low TSH levels may result from their relatively modest degree of overtreatment.

Vitamin D and its role in skeletal muscle.

This review discusses the clinical and laboratory studies that have examined a role of vitamin D in skeletal muscle. Many observational studies, mainly in older populations, indicate that vitamin D status is positively associated with muscle strength and physical performance and inversely associated with risk of falling. Clinical trials of vitamin D supplementation in older adults with low vitamin D status mostly report improvements in muscle performance and reductions in falls. The underlying mechanisms are probably both indirect via calcium and phosphate and direct via activation of the vitamin D receptor (VDR) on muscle cells by 1,25-dihydroxyvitamin D [1,25(OH)2D]. VDR activation at the genomic level regulates transcription of genes involved in calcium handling and muscle cell differentiation and proliferation. A putative membrane-associated VDR activates intracellular signaling pathways also involved in calcium handling and signaling and myogenesis. Additional evidence comes from VDR knockout mouse models with abnormal muscle morphology and physical function, and VDR polymorphisms which are associated with differences in muscle strength. Recent identification of CYP27B1 bioactivity in skeletal muscle cells and in regenerating adult mouse muscle lends support to the direct action of both 25-hydroxyvitamin D and 1,25(OH)2D in muscle. Despite these research advances, many questions remain. Further research is needed to fully characterize molecular mechanisms of vitamin D action on muscle cells downstream of the VDR, describe the effects on muscle morphology and contractility, and determine whether these molecular and cellular effects translate into clinical improvements in physical function.

Leptin, Body Composition and Bone Mineral Density in Premenopausal Women

Body weight is known to be associated with bone mass, however, it is unclear whether body composition, as reflected by the percent of total weight that is fat tissue (%fat), is associated with bone mass independently of weight. Fat tissue is metabolically active, and hormonal factors may mediate an association of %fat with bone mass. Leptin, a hormone produced in fat tissue, has recently been shown to be inversely related to bone mass in mice, but whether it is related to human bone mass is uncertain. We sought to investigate the associations of %fat and of serum leptin concentration with bone mineral density (BMD) in a cohort of 153 premenopausal women. BMD measurements of the total hip, lumbar spine and total body as well as body composition were measured by dual energy X-ray absorptiometry (DXA). Serum leptin levels were established using a commercial competitive binding assay. Individually, body weight, %fat and leptin were each positively associated with BMD at all three sites. However, when we examined BMD either as a function of both body weight and %fat together, or as a function of both body weight and leptin together, we found that for a given body weight, BMD appeared to be inversely associated with %fat and similarly appeared to be inversely associated with leptin. When BMD was examined as a function of %fat and leptin together, we found that for a given %fat, leptin appeared to be inversely associated with BMD. In summary, the results of this study suggest that for a given body weight, a higher proportion of fat and a higher serum leptin concentration have negative associations with bone mass in premenopausal women.

Influence of Body Weight on Rates of Change in Bone Density of the Spine, Hip, and Radius in Postmenopausal Women

SummaryInterrelationships between percent of ideal body weight (%IBW), serum estrogen levels, and change in bone mineral density (ΔBMD) and bone mineral content (ΔBMC) were studied in 288 postmenopausal women aged 41–71 years who participated in a 2-year calcium supplement trial. The spine (L2–L4) and femoral neck were measured by dualphoton absorptiometry, and the radius was measured by single-photon absorptiometry. Years since menopause, calcium intake, and initial BMD or BMC were included as independent variables in two-phase regressions of ΔBMD and ΔBMC on %IBW. Increased %IBW protected against loss of spine BMD [regression slope estimate=0.05, 95% C.I.: (0.03, 0.26)] and BMC in women up through about 106 %IBW but not in heavier women. Increased %IBW was not significantly related to ΔBMD or ΔBMC at the femoral neck or radius. Women above 106%IBW had significant gains in spine and femoral neck area (P< 0.05). Serum estrone and estradiol were positively correlated with ΔBMD and ΔBMC at the femoral neck only.

A Randomized Study on the Effect of Vitamin D3 Supplementation on Skeletal Muscle Morphology and Vitamin D Receptor Concentration in Older Women

CONTEXT Studies examining whether vitamin D supplementation increases muscle mass or muscle-specific vitamin D receptor (VDR) concentration are lacking. OBJECTIVE Our objective was to determine whether vitamin D₃ 4000 IU/d alters muscle fiber cross-sectional area (FCSA) and intramyonuclear VDR concentration over 4 months. DESIGN AND SETTING This was a randomized, double-blind, placebo-controlled study in a single center. PARTICIPANTS Participants were 21 mobility-limited women (aged ≥ 65 years) with serum 25-hydroxyvitamin D (25OHD) levels of 22.5 to 60 nmol/L. MAIN OUTCOME MEASURES Baseline and 4-month FCSA and intramyonuclear VDR were measured from vastus lateralis muscle cross-sections probed for muscle fiber type (I/IIa/IIx) and VDR using immunofluorescence. RESULTS At baseline, mean (±SD) age was 78 ± 5 years; body mass index was 27 ± 5 kg/m², 25OHD was 46.3 ± 9.5 nmol/L, and a short physical performance battery score was 7.95 ± 1.57 out of 12. At 4 months, 25OHD level was 52.5 ± 17.1 (placebo) vs 80.0 ± 11.5 nmol/L (vitamin D [VD]; P < .01), and change in 25OHD level was strongly associated with percent change in intramyonuclear VDR concentration-independent of group (r = 0.87, P < .001). By treatment group, percent change in intramyonuclear VDR concentration was 7.8% ± 18.2% (placebo) vs 29.7% ± 11.7% (VD; P = .03) with a more pronounced group difference in type II vs I fibers. Percent change in total (type I/II) FCSA was -7.4% ± 18.9% (placebo) vs 10.6% ± 20.0% (VD; P = .048). CONCLUSION Vitamin D₃ supplementation increased intramyonuclear VDR concentration by 30% and increased muscle fiber size by 10% in older, mobility-limited, vitamin D-insufficient women. Further work is needed to determine whether the observed effect of vitamin D on fiber size is mediated by the VDR and to identify which signaling pathways are involved.

Treatment with Potassium Bicarbonate Lowers Calcium Excretion and Bone Resorption in Older Men and Women

CONTEXT Bicarbonate has been implicated in bone health in older subjects on acid-producing diets in short-term studies. OBJECTIVE The objective of this study was to determine the effects of potassium bicarbonate and its components on changes in bone resorption and calcium excretion over 3 months in older men and women. DESIGN, PARTICIPANTS, AND INTERVENTION In this double-blind, controlled trial, 171 men and women age 50 and older were randomized to receive placebo or 67.5 mmol/d of potassium bicarbonate, sodium bicarbonate, or potassium chloride for 3 months. All subjects received calcium (600 mg of calcium as triphosphate) and 525 IU of vitamin D(3) daily. MAIN OUTCOME MEASURES Twenty-four-hour urinary N-telopeptide and calcium were measured at entry and after 3 months. Changes in these measures were compared across treatment groups in the 162 participants included in the analyses. RESULTS Bicarbonate affected the study outcomes, whereas potassium did not; the two bicarbonate groups and the two no bicarbonate groups were therefore combined. Subjects taking bicarbonate had significant reductions in urinary N-telopeptide and calcium excretion, when compared with subjects taking no bicarbonate (both before and after adjustment for baseline laboratory value, sex, and changes in urinary sodium and potassium; P = 0.001 for both, adjusted). Potassium supplementation did not significantly affect N-telopeptide or calcium excretion. CONCLUSIONS Bicarbonate, but not potassium, had a favorable effect on bone resorption and calcium excretion. This suggests that increasing the alkali content of the diet may attenuate bone loss in healthy older adults.