David R. Fraser

School-milk intervention trial enhances growth and bone mineral accretion in Chinese girls aged 10-12 years in Beijing.

A 2-year milk intervention trial was carried out with 757 girls, aged 10 years, from nine primary schools in Beijing (April 1999 - March 2001). Schools were randomised into three groups: group 1, 238 girls consumed a carton of 330 ml milk fortified with Ca on school days over the study period; group 2, 260 girls received the same quantity of milk additionally fortified with 5 or 8 microg cholecalciferol; group 3, 259 control girls. Anthropometric and bone mineralisation measurements, as well as dietary, health and physical-activity data, were collected at baseline and after 12 and 24 months of the trial. Over the 2-year period the consumption of this milk, with or without added cholecalciferol, led to significant increases in the changes in height (> or =0.6 %), sitting height (> or =0.8 %), body weight (> or 2.9 %), and (size-adjusted) total-body bone mineral content (> or =1.2 %) and bone mineral density (> or =3.2 %). Those subjects receiving additional cholecalciferol compared with those receiving the milk without added 25-hydoxycholecalciferol had significantly greater increases in the change in (size-adjusted) total-body bone mineral content (2.4 v. 1.2 %) and bone mineral density (5.5 v. 3.2 %). The milk fortified with cholecalciferol significantly improved vitamin D status at the end of the trial compared with the milk alone or control groups. It is concluded that an increase in milk consumption, e.g. by means of school milk programmes, would improve bone growth during adolescence, particularly when Ca intake and vitamin D status are low.

Low vitamin D status is associated with physical inactivity, obesity and low vitamin D intake in a large US sample of healthy middle-aged men and women

The aim of this study was to investigate modifiable predictors of vitamin D status in healthy individuals, aged 55-74, and living across the USA. Vitamin D status [serum 25-hydroxyvitamin D (25(OH)D)] was measured along with age and season at blood collection, demographics, anthropometry, physical activity (PA), diet, and other lifestyle factors in 1357 male and 1264 female controls selected from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) cohort. Multivariate linear and logistic regression analyses were used to identify associations with vitamin D status. Three%, 29% and 79% of the population had serum 25(OH)D levels<25, <50 and <80 nmol/L, respectively. The major modifiable predictors of low vitamin D status were low vitamin D dietary and supplement intake, body mass index (BMI) >30 kg/m2, physical inactivity (PA) and low milk and calcium supplement intake. In men, 25(OH)D was determined more by milk intake on cereal and in women, by vitamin D and calcium supplement and menopausal hormone therapy (MHT) use. Thus targeting an increase in vigorous activity and vitamin D and calcium intake and decreasing obesity could be public health interventions independent of sun exposure to improve vitamin D status in middle-aged Americans.

Low Vitamin D Status Has an Adverse Influence on Bone Mass, Bone Turnover, and Muscle Strength in Chinese Adolescent Girls

Our goal in this cross-sectional study was to investigate the influence of low-vitamin D status on bone mass, bone turnover, and muscle strength in 301 healthy Chinese adolescent girls. Blood plasma 25-hydroxyvitamin D [25(OH)D] was measured by RIA and plasma and urine biomarkers of bone turnover were measured. Bone mineral content (BMC) and density and bone area for the whole body and the distal and proximal forearm were measured by dual energy X-ray absorptiometry. When vitamin D deficiency was defined as a serum 25(OH)D concentration of < or =50 nmol/L and severe deficiency as <25 nmol/L, 57.8% of subjects were vitamin D deficient and 31.2% were severely deficient. Multivariate analysis shows that girls with adequate vitamin D status had higher size-adjusted BMC for the whole body (P < 0.001), distal forearm (P < 0.001), and proximal forearm (P < 0.01) than those with poorer vitamin D status after adjusting for body size, handgrip strength, physical activity, and dietary intakes of calcium and vitamin D. Similar results were also found for handgrip muscle strength. Participants with adequate vitamin D status had significantly lower concentrations of bone alkaline phosphatase in plasma and deoxypyridinoline:creatinine ratio in urine compared with those of the vitamin D-deficient girls. Adolescent girls with adequate vitamin D status had significantly higher bone mass and muscle strength compared with those with poor vitamin D status. This may be attributed in part to a lower rate of bone remodeling with adequate vitamin D status. These findings suggest that adequate vitamin D status during adolescence is important for optimizing bone mass, which may lead to higher peak bone mass at maturity. Poor vitamin D status also compromises forearm muscle strength.

Vitamin D-Deficiency In Asia

Vitamin D-deficiency rickets is an important disease of childhood in China. It occurs in all regions (20-53 degrees N) but is more prevalent in the north. A survey in Beijing indicated that Vitamin D-deficiency (plasma 25(OH)D concentration <12.5 nmol/l) occurred in more than 40% of adolescent girls in winter. Dietary calcium was often as low as 350 mg per day and a positive correlation was found between this and both bone mineral density (BMD) and Vitamin D status. In a subsequent intervention study with 757 Beijing schoolgirls, a daily supplement of milk, fortified with calcium, was provided on school days for 24 months. From anthropometric and bone density data, it is evident that the increased calcium intake from milk, had significant effects on bone and that deficiencies of both calcium and of Vitamin D had been affecting bone growth and development. In neighboring Mongolia (42 degrees -50 degrees N), rickets is also common, but its prevalence has increased since 1990. A 2-year survey (2000-2002) in Mongolia indicated that, as in China, a low intake of calcium and limited exposure to solar ultraviolet (UV) light in summer were associated with Vitamin D-deficiency. However, over the last decade, malnutrition has become widespread. It now appears that malnutrition impairs the efficiency of the utilization of Vitamin D obtained in summer. Hence, a number of factors need to be addressed to prevent Vitamin D-deficiency during growth.

The Vitamin D Receptor (VDR) Is Expressed in Skeletal Muscle of Male Mice and Modulates 25-Hydroxyvitamin D (25OHD) Uptake in Myofibers

Vitamin D deficiency is associated with a range of muscle disorders, including myalgia, muscle weakness, and falls. In humans, polymorphisms of the vitamin D receptor (VDR) gene are associated with variations in muscle strength, and in mice, genetic ablation of VDR results in muscle fiber atrophy and motor deficits. However, mechanisms by which VDR regulates muscle function and morphology remain unclear. A crucial question is whether VDR is expressed in skeletal muscle and directly alters muscle physiology. Using PCR, Western blotting, and immunohistochemistry (VDR-D6 antibody), we detected VDR in murine quadriceps muscle. Detection by Western blotting was dependent on the use of hyperosmolar lysis buffer. Levels of VDR in muscle were low compared with duodenum and dropped progressively with age. Two in vitro models, C2C12 and primary myotubes, displayed dose- and time-dependent increases in expression of both VDR and its target gene CYP24A1 after 1,25(OH)2D (1,25 dihydroxyvitamin D) treatment. Primary myotubes also expressed functional CYP27B1 as demonstrated by luciferase reporter studies, supporting an autoregulatory vitamin D-endocrine system in muscle. Myofibers isolated from mice retained tritiated 25-hydroxyvitamin D3, and this increased after 3 hours of pretreatment with 1,25(OH)2D (0.1nM). No such response was seen in myofibers from VDR knockout mice. In summary, VDR is expressed in skeletal muscle, and vitamin D regulates gene expression and modulates ligand-dependent uptake of 25-hydroxyvitamin D3 in primary myofibers.

UK Food Standards Agency Workshop Report: an investigation of the relative contributions of diet and sunlight to vitamin D status.

The UK Food Standards Agency (FSA) convened an international group of scientific experts to review three Agency-funded projects commissioned to provide evidence for the relative contributions of two sources, dietary vitamin D intake and skin exposure to UVB rays from sunlight, to vitamin D status. This review and other emerging evidence are intended to inform any future risk assessment undertaken by the Scientific Advisory Committee on Nutrition. Evidence was presented from randomised controlled trials to quantify the amount of vitamin D required to maintain a serum 25-hydroxy vitamin D (25OHD) concentration >25 nmol/l, a threshold that is regarded internationally as defining the risk of rickets and osteomalacia. Longitudinal evidence was also provided on summer sunlight exposure required to maintain 25OHD levels above this threshold in people living in the British Isles (latitude 51 degrees-57 degrees N). Data obtained from multi-level modelling of these longitudinal datasets showed that UVB exposure (i.e. season) was the major contributor to changes in 25OHD levels; this was a consistent finding in two Caucasian groups in the north and south of the UK, but was less apparent in the one group of British women of South Asian origin living in the south of the UK. The FSA-funded research suggested that the typical daily intake of vitamin D from food contributed less than UVB exposure to average year-round 25OHD levels in both Caucasian and Asian women. The low vitamin D status of Asian women has been acknowledged for some time, but the limited seasonal variation in Asian women is a novel finding. The Workshop also considered the dilemma of balancing the risks of vitamin D deficiency (from lack of skin exposure to sunlight in summer) and skin cancer (from excessive exposure to sunlight with concomitant sunburn and erythema). Cancer Research UK advises that individuals should stay below their personal sunburn threshold to minimise their skin cancer risk. The evidence suggests that vitamin D can be produced in summer at the latitude of the UK, with minimal risk of erythema and cell damage, by exposing the skin to sunlight for a short period at midday, when the intensity of UVB is at its daily peak. The implications of the new data were discussed in the context of dietary reference values for vitamin D for the general population aged 4-64 years. Future research suggestions included further analysis of the three FSA-funded studies as well as new research.

Milk consumption and bone mineral content in chinese adolescent girls

A cross-sectional study of a random sample of 649 girls, aged 12-14 years (mean +/- SD: 12.9 +/- 0.6 years), in the Beijing area examined the relationship between diet and bone mineral status. Food and nutrient intakes over the past year were estimated by means of a semiquantitative food frequency questionnaire. Bone mineral content (BMC) and bone width (BW) at the distal one-third and one-tenth radius and ulna were measured by single-photon absorptiometry. Results showed Beijing pubertal girls had a low mean milk consumption (fresh and powdered milk, vitamin D-fortified milk, and yogurt) at 50 g/day (95% confidence interval [CI] 44-55 g/day whereas one-third consumed no milk at all. Mean calcium intake was 356 +/- 97 mg/day of which only 21% was provided by milk and milk products. Milk intake varied by region (rural, suburban, and urban: 9, 36, and 83 g/day, respectively, p < 0.0005) as did the proportion of milk consumers in the three areas (30%, 64%, and 91%, p < 0.0005). Bone mineral density (BMD) at the distal one-third and one-tenth radius and one-tenth ulna was positively associated with milk consumption (p < 0.05). Multiple regression analysis of BMC on foods and nutrients as well as confounding factors, including weight, bone age, Tanner stage, and School Physical Activity Score (SPAS), showed that milk intake was the only dietary factor included in the models for BMC at the four bone sites measured. The model explained 54%-65% of the variation in BMC, and milk alone accounted for up to 3.2% of the variation. Milk was the only food group with significant partial correlation with BMC. SPAS, weight, bone age, and Tanner stage each accounted for a smaller variation in BMC (<1.8%). The results indicate that milk (presumably as an integrated source of nutrients) had a beneficial effect on bone mass of Beijing pubertal girls and was a better nutritional determinant of BMC than intake of any milk nutrient alone. Promotion of milk consumption should be considered for achieving optimal bone mass in this population group.

Evidence for a Specific Uptake and retention Mechanism for 25- Hydroxyvitamin D (25OHD) in skeletal Muscle Cells

Little is known about the mechanism for the prolonged residence time of 25-hydroxyvitamin D (25OHD) in blood. Several lines of evidence led us to propose that skeletal muscle could function as the site of an extravascular pool of 25OHD. In vitro studies investigated the capacity of differentiated C2 murine muscle cells to take up and release 25OHD, in comparison with other cell types and the involvement of the membrane protein megalin in these mechanisms. When C2 cells are differentiated into myotubes, the time-dependent uptake of labeled 25OHD is 2-3 times higher than in undifferentiated myoblasts or nonmuscle osteoblastic MG63 cells (P < .001). During in vitro release experiments (after 25OHD uptake), myotubes released only 32% ± 6% stored 25OHD after 4 hours, whereas this figure was 60% ± 2% for osteoblasts (P < .01). Using immunofluorescence, C2 myotubes and primary rat muscle fibers were, for the first time, shown to express megalin and cubilin, endocytotic receptors for the vitamin D binding protein (DBP), which binds nearly all 25OHD in the blood. DBP has a high affinity for actin in skeletal muscle. A time-dependent uptake of Alexafluor-488-labeled DBP into mature muscle cells was observed by confocal microscopy. Incubation of C2 myotubes (for 24 hours) with receptor-associated protein, a megalin inhibitor, led to a 40% decrease in 25OHD uptake (P < .01). These data support the proposal that 25OHD, after uptake into mature muscle cells, is held there by DBP, which has been internalized via membrane megalin and is retained by binding to actin.

Influence of body composition, muscle strength, diet and physical activity on total body and forearm bone mass in Chinese adolescent girls

The aim of the present study was to determine association between body composition, muscle strength, diet and physical exercise with bone mineral content (BMC) and bone area (BA) in 283 Chinese adolescent girls aged 15 years in Beijing, China. Body composition, pubertal stage, physical activity and dietary intakes were assessed using standard validated protocols. Total body and forearm bone, lean body mass (LBM) and fat body mass (FBM) were determined by dual X-ray absorptiometry. Multivariate linear regression analyses were carried out to examine the predictors of BMC and BA, after controlling for potential confounders. The subjects had a mean age of 15.0 (sd 0.9) years and 99.6 % of them had reached menarche. Multivariate analyses showed that LBM, FBM, handgrip muscle strength and milk intake were significant independent determinants of BMC and BA of the total body and/or forearm sites. LBM was found to be a stronger independent determinant than FBM of BMC and BA, whereas handgrip muscle strength was only found as significant determinant of BMC and BA at the forearm sites than in total body BMC and BA. Further, total physical activity level had a significant positive association with handgrip and LBM. This suggested that greater muscle strength and higher LBM may reflect higher levels of physical activity. Therefore, continuous healthy lifestyle practices such as adequate intake of milk and continuous participation in physical activity should be encouraged throughout adolescence to optimise bone growth during this period.

Effects of diet and exercise on plasma vitamin D (25(OH)D) levels in Vietnamese immigrant elderly in Sydney, Australia

Vitamin D deficiency may be associated with osteoporosis and fractures in the elderly. In Australia where there is a sizeable Vietnamese population, research has not yet clarified the roles of diet, exercise and sun exposure in determining vitamin D status. Plasma samples for 25-hydroxy-vitamin D (25(OH)D); dietary intake of vitamin D and calcium; muscle strength and sun exposure were measured and weekly dairy intake, exercise levels and smoking habits were surveyed in free-living elderly of Vietnamese and Australian/British origin. There was marginal vitamin D deficiency (<37 nmol/L 25(OH)D) in 63% of Vietnamese but only in 37% of Australian/British born. Low dairy intake and no vigorous exercise were best predictors of vitamin D deficiency in Vietnamese, taking into account age, gender, dietary intake and sun exposure. Since these migrant elderly may not get adequate sun exposure due to either clothing customs or cultural norms that encourage fair (untanned) skin, it is important to encourage increased exercise and dairy intake.