The life-course association between socioeconomic inequalities and bone health is becoming well-documented. Yet, little is known about the impact of socioeconomic factors on bone-related proinflammatory cytokines in the years before the achievement of peak bone mass. We aimed to systematically identify and synthesise existing data to investigate the relationship between household income, an important parameter of socioeconomic status (SES) known to influence child health, and bone-related pro-inflammatory cytokines during the years prior to peak bone mass attainment (ages 6 to 30 years).
We applied a defined e-search strategy to the PubMed, Ovid (Medline), EMBASE, PsycINFO and CINAHL databases, with no set limits of publication date. All full-text peer-reviewed articles written in English that encompassed household income data and levels of proinflammatory cytokines associated with bone accrual (C-reactive protein [CRP], interleukin-6 [IL-6], and tumour necrosis factor-alpha [TFN-a]) were screened for eligibility; epidemiological cross-sectional, case-control, and/or cohort studies in children and young adults aged 6-30 years, and baseline data from randomised control trials, where relevant, were included. The Lievense et al.1 scoring system was used to determine the level of evidence.
In total, 14 studies met the inclusion criteria; 4 cohort studies (from USA and Australia) and 10 cross-sectional studies (from USA, Puerto Rico and Canada). These studies included a total of 52,586 participants (~54% female). We found limited evidence for an association between low household income and higher levels of IL-6. However, moderate-strong evidence was observed regarding a lack of association between TFN-a and CRP, respectively.
This review suggests that an association may exist between low household income with increased levels of IL-6, although based on a paucity of data. Future analyses should investigate associations between alternate parameters of SES and proinflammatory cytokines, given the importance of early life influences on later life bone health.
[1] Lievense A, Bierma-Zeinstra SMA, Vergahen AP, van Baar ME, Verhaar JAN, Koes BW (2002) Influence of obesity on the development of osteoarthritis of the hip: a systematic review. Rheumatol 41:1155–1162