Fasting glucose, bone area and bone mineral density: a Mendelian randomisation study

AIMS/HYPOTHESIS

Observational studies indicate that type 2 diabetes mellitus and fasting glucose levels are associated with a greater risk for hip fracture, smaller bone area and higher bone mineral density (BMD). However, these findings may be biased by residual confounding and reverse causation. Mendelian randomisation (MR) utilises genetic variants as instruments for exposures in an attempt to address these biases. Thus, we implemented MR to determine whether fasting glucose levels in individuals without diabetes are causally associated with bone area and BMD at the total hip.

METHODS

We selected 35 SNPs strongly associated with fasting glucose (p < 5 × 10^-8) in a non-diabetic European-descent population from the Meta-Analyses of Glucose and Insulin-related traits Consortium (MAGIC) (n = 133,010). MR was used to assess the associations of genetically predicted fasting glucose concentrations with total hip bone area and BMD in 4966 men and women without diabetes from the Swedish Mammography Cohort, Prospective Investigation of Vasculature in Uppsala Seniors and Uppsala Longitudinal Study of Adult Men.

RESULTS

In a meta-analysis of the three cohorts, a genetically predicted 1 mmol/l increment of fasting glucose was associated with a 2% smaller total hip bone area (-0.67 cm² [95% CI -1.30, -0.03; p = 0.039]), yet was also associated, albeit without reaching statistical significance, with a 4% higher total hip BMD (0.040 g/cm² [95% CI -0.00, 0.07; p = 0.060]).

CONCLUSIONS/INTERPRETATION

Fasting glucose may be a causal risk factor for smaller bone area at the hip, yet possibly for greater BMD. Further MR studies with larger sample sizes are required to corroborate these findings.

Longitudinal changes in bone mineral density, bone mineral content and bone area at the lumbar spine and hip in postmenopausal women, and the influence of abdominal aortic calcification

Longitudinal studies often report that spine bone mineral density (BMD), measured by DXA, is stable in older adults, which has been attributed to osteophyte development and the presence of aortic calcification. A decline in projected spine area as a result of loss of intervertebral disc height might also contribute to higher BMD. We utilised data from 297 postmenopausal women (mean 73 years) who had DXA measurements of the lumbar spine, total hip and femoral neck 5 years apart, and abdominal aortic calcification scoring from vertebral morphometry. BMD declined by -4.4% at the total hip and -3.9% at the femoral neck (p < 0.001), but did not change at the spine (-0.5%, p = 0.12). In contrast, bone mineral content (BMC) declined by -4.0% at the total hip, -2.5% at the femoral neck and -1.7% at the spine (all p < 0.001). Bone area increased by 0.5% at the hip and 1.6% at the femoral neck but declined by -1.2% at the spine (all p < 0.001). 43% of the cohort had abdominal aortic calcification (AAC) present at baseline. The presence of AAC at baseline was not related to changes in BMD or BMC at the total hip or femoral neck, nor to BMD at the spine. However, women with AAC present had a smaller loss of BMC at the spine than those without (-0.8% versus -2.4%, p = 0.03). AAC score increased more over 5 years among those with AAC at baseline than those without (0.28 versus 0.16, p = 0.036). Thus, the stability of spine BMD is the result of both a loss of projected bone area (as a result of intervertebral disc changes and/or a decrease in projected area of the vertebral bodies) and the effects of aortic calcification. Future clinical trials should consider assessing changes in spine BMC as a more informative index of spine mineral status.

Judo Practice in Early Age Promotes High Level of Bone Mass Acquisition of Growing Boys' Skeleton

The current study aimed to exhibit effects of judo training for at least 2 yr on bone mass parameters in growing boys. Our population was composed of one hundred and thirty boys in tanner stage 1 and aged 10.52 ± 0.86 yr. Eleven judo players were therefore, excluded from the study because they do not have participate regularly to the judo training sessions during the last 2 yr. The resting sample was divided into two groups: 50 judo players (JU group) and 69 controls (C group). Bone mineral density (BMD), bone mineral content (BMC), and bone area (BA) were evaluated by using dual-photon X-ray absorptiometry on weight-bearing sites: the whole body, lumbar spine (L2-L4), legs, femoral necks and hips and on the non-weight bearing sites: arms and radiuses. Our findings displayed that judo participation was markedly associated with greater values of bone mass parameters in young judo players than control group. Accordingly, the BMD and BA results exhibited significant differences in the whole body, legs, dominant total hip, arms and both whole radiuses in addition to the dominant femoral neck, the non-dominant total hip and except the non-dominant whole radius for the BMC parameter. Additionally, data of the subject within t test has shown significant differences of bone mass parameters only in the non weight-bearing sites in the judo players without any obvious variation in the controls. Differences of BMD observed on the dominant arm and whole radius in addition to the increased BMC values showed in the dominant whole radius compared with their contra-lateral sites in judo players without any marked variation of BA parameters in all sites in both groups. In growing boys, judo practice was obviously associated with osteogenic effects in specific sites.

Handball Practice Enhances Bone Mass in Specific Sites Among Prepubescent Boys

This investigation's purpose is to focus on the effects of practicing handball for at least 2 yr on bone acquisition among prepubescent boys. One hundred prepubescent boys aged 10.68 ± 0.85 yr were divided into 2 groups: 50 handball players (HP group) and 50 controls (C group). Bone mineral density (BMD), bone mineral content (BMC), and bone area (BA) were evaluated by using dual-photon X-ray absorptiometry on the whole body, lumbar spine (L2-L4), legs, arms, femoral necks, hips and radiuses. Results showed greater values of BMD in both right and left femoral neck and total hip in handball players than in controls. In addition, handball players had higher values of legs and right total hip BMC than controls without any obvious variation of BA measurement in all sites between groups. All results of the paired t-test displayed an obviously marked variation of bone mass parameters between the left and right sides in the trained group without any marked variation among controls. Data showed an increased BMD of the supporting sites between the left and the right leg among handball players. However, "BMC" results exhibited higher values in the right than in the left total hip, and in the right total radius than in the left correspondent site. In addition, differences in the "BA" measurements were observed in the left total hip and in the right arm. Specific bone sites are markedly stimulated by handball training in prepubescent boys.

Associations between adiposity, hormones, and gains in height, whole-body height-adjusted bone size, and size-adjusted bone mineral content in 8- to 11-year-old children

We examined fat-independent associations of hormones with height and whole-body bone size and mineral content in 633 school children. IGF-1 and osteocalcin predict growth in height, while fat, osteocalcin, and in girls also, IGF-1 predict growth in bone size. Leptin and ghrelin are inversely associated with bone size in girls.

INTRODUCTION

Obesity causes larger bone size and bone mass, but the role of hormones in this up-regulation of bone in obesity is not well elucidated. We examined longitudinal associations between baseline body fat mass (FM), and fat-independent fasting levels of ghrelin, adiponectin, leptin, insulin, insulin-like growth factor-I (IGF-1), osteocalcin, and intact parathyroid hormone, and subsequent changes in height and in whole-body height-adjusted bone area "BAheight" and size-adjusted bone mineral content "BMCsize" in 8- to 11-year-olds.

METHODS

Analyses were carried out separately for boys (n = 325) and girls (n = 308) including data from baseline, 3 and 6 months from OPUS School Meal Study.

RESULTS

In both sexes: gain in BAheight was positively associated with baseline FM (≥2.05 cm(2)/kg, both p ≤ 0.003). Furthermore, gain in height was positively associated with baseline IGF-1 (≥0.02 cm/ng/ml, p = 0.001) and osteocalcin (≥0.13 cm/ng/ml, p ≤ 0.009); and gain in BAheight was positively associated with baseline osteocalcin (≥0.35 cm(2)/ng/ml, p ≤ 0.019). In girls only, gain in BAheight was also positively associated with baseline IGF-1 (0.06 cm(2)/ng/ml, p = 0.017) and inversely associated with both baseline ghrelin (-0.01 cm(2)/pg/ml, p = 0.001) and leptin (-1.21 cm(2)/μg/ml, p = 0.005). In boys, gain in BMCsize was positively associated with osteocalcin (0.18 g/ng/ml, p = 0.030).

CONCLUSIONS

This large longitudinal study suggests that in 8- to 11-year-old children, IGF-1 and osteocalcin predict growth in height, while FM, osteocalcin, and in girls also, IGF-1 predict growth in BAheight. Fat-independent inverse associations of leptin and ghrelin with BAheight in girls' are contrary to proposed growth-stimulating effects of leptin. Osteocalcin in boys predicts gain in BMCsize.