Impact of weight-bearing and sex-stratified differences in risk factors of bone loss on bone mineral density in HIV conditions - findings of the Nigeria HIV-BMD study: An observational study

BackgroundBiomechanical loading exerts an osteogenic stimulus; thus, bone mineral density(BMD) may vary in weight-bearing and non-weight-bearing bones. Therefore, weight-bearing activities could modulate sex-, HAART- and HIV-related BMD loss. MethodA cross-sectional observational study of 503 people living with HIV (PLWH) selected by convenience sampling at Enugu State University Teaching Hospital, Nigeria, was conducted from September 2015 to September 2016. The BMD of toe or weight-bearing(BMDtoe) and thumb or non-weight-bearing(BMDthumb) bones were measured with Xrite 331C densitometer and compared using independent t-test. Impact of the risk factors (age, weight, body mass index-BMI, duration of HIV, height and types of HAART) of bone loss and their relationships with the BMD were compared across the sexes using multivariate, and univariate regression analyses, at p<0.05,two-tailed. ResultParticipants comprised of females(378/75.1%), males(89/17.7%) and others(36/7.16%) without gender specificity, with mean age=37.2{+/-}9.79years, and BMI=25.6{+/-}5.06kg/m. HAART-experienced participants (352/69.98%) mean HAART-exposure duration was 4.54{+/-}3.51years. BMDtoe(-0.16{+/-}0.65g/cm3) was higher(p<0.05) than BMDthumb(-0.93{+/-}0.44g/cm3), and differed across the BMI classes (p=0.000003;d=0.998), and was accounted for in post hoc analysis by normal weight versus underweight BMI classes (p=<0.001). BMDtoe was positively correlated with height (r=0.13,r2=0.0169;p<0.05), and males were taller than females(p<0.001). Females accounted for 90%(9/10) cases of osteopenia and 71.43%(5/7) osteoporosis. Males were older(p=0.002) while females had greater BMI (p=0.02), lower median BMDtoe(p=0.005) and BMDthumb (p=0.005). ConclusionHigher BMD in weight-bearing bones, and lower BMDtoe in underweight (sub-optimal loading) BMI class suggest a role for osteogenic stimulus and fat metabolism in bone loss. Females being younger/heavier, would have greater loading/osteogenic stimulus reinforced by lesser age-related BMD changes. Males being taller would have greater bone marrow adipose tissue that promote osteogenesis through paracrine mechanisms. Therefore, higher BMD in males should be partly explained by height-related metabolic surrogates and sex-hormonal differences. Greater BMD In females weight-bearing bones implies that loading ameliorates physiological tendencies towards lower BMD.