The association between resting autonomic nervous system activity and bone mineral density in older adults

Elevated sympathetic nervous system activity has been shown to have a detrimental effect on bone mass in animal studies, whereas parasympathetic activity is thought to exert a protective effect. However, little is known about the relationship between autonomic nervous system activity and bone health in humans. This study aimed to investigate the relationship between resting autonomic nervous system activity and areal BMD (aBMD) or volumetric BMD (vBMD) in older adults.

A total of 119 older adults (27 men, 92 women) were included in this cross-sectional study. Participants underwent DXA scans of the left hip and lumbar spine (L1-4) as well as, pQCT scans at the 4% and 38% left tibia sites. Sympathetic activity was evaluated using non-invasive skin sympathetic nerve activity and galvanic skin response. Parasympathetic activity was evaluated using time-domain and frequency-domain heart rate variability metrics. Multiple linear regression models adjusted for sex, age, lifetime bone-relevant physical activity and BMI, were used to examine associations between resting sympathetic and parasympathetic nervous system activity and BMD (primary analysis) or vBMD (secondary analysis). P values were adjusted using the Benjamini-Hochberg procedure to control the false discovery rate (FDR).

None of the primary aBMD associations were significant following FDR correction. Higher integrated skin sympathetic nerve activity burst area was negatively associated with total hip aBMD before correction (β = -0.214, P = 0.008; FDR-adjusted P = 0.062). In the secondary analysis, the skin conductance response frequency was negatively associated with trabecular vBMD at the 4% tibial site (β = -0.354, P = 0.001; FDR-adjusted P = 0.004). Parasympathetic nerve activity was not associated with aBMD or vBMD.

The primary aBMD hypotheses were not supported following correction for multiple comparisons. Exploratory associations between elevated sympathetic activity and lower areal and volumetric BMD warrants further investigation as a factor in age-related bone loss.