The association between reproductive hormones and asthma-related outcomes in boys in the rural Western Cape Province, South Africa

Background. Asthma is more prevalent and severe among boys than girls, but this pattern reverses after puberty. It has been suggested that reproductive hormones may play a role in explaining these sex differences after puberty. However, the evidence for this relationship remains limited, as there have been no previous studies conducted on children in low- and middle-income countries on several reproductive endocrine hormones. Objective. To investigate the association between reproductive endocrine hormones and asthma-related outcomes among boys residing in a rural setting. Methods. Data on asthma outcomes and hormone levels were analysed from a cross-sectional study of 314 boys (aged 6 - 18 years) in the rural Western Cape Province, South Africa (SA). These were collected using an abbreviated International Study of Asthma and Allergies in Childhood questionnaire. Testosterone (total serum testosterone (TST) and free testosterone (FT)), luteinising hormone (LH), serum follicle- stimulating hormone (FSH), oestradiol and serum hormone-binding globulin (SHBG) were assessed using electrochemiluminescence immunoassays. Results. Current wheezing (CW), asthma symptom score ≥2 and parental-reported asthma (PA) prevalence were 6.1%, 6.7% and 8.0%, respectively. Multivariate analysis showed that increasing levels of detected TST were significantly negatively associated with CW (odds ratio (OR) 0.66, 95% confidence interval (CI) 0.45 - 0.98) and asthma symptom score (OR 0.64, 95% CI 0.43 - 0.95), while no statistically significant association was observed for PA (OR 0.86, 95% CI 0.59 - 1.25). FT levels showed an inverse association with all asthma- related outcomes, with a statistically significant association with asthma symptom score. Similar associations were found for FSH, while associations with LH were less consistent across outcomes, and no association was observed for oestradiol and SHBG. Conclusion. Our findings suggest that increasing serum testosterone levels (including those in the normal range and those above the normal range) detected among boys from rural settings in the Western Cape Province, SA, are associated with a reduced risk of asthma after adjusting for important underlying risk factors.