Fluctuations in income amplify risk of cardiovascular diseases, death
Income volatility and income drops over the long-term appear to increase the risk of cardiovascular diseases (CVD) and all-cause mortality in young adults, according to a recent US study.
“The findings of this study reinforce the urgency and growing public health threat associated with income volatility,” said researchers. “Given the current economic environment of increasing income instability, understanding how income volatility is associated with health has become increasingly important.”
A total of 3,913 young adults (mean age 30.0±3.6 years; 56.2 percent female) were enrolled in 1985–1986 and were followed until 2005. Of the participants, 248 experienced ≥2 income drops, defined as an income decrease of ≥25 percent compared with the previous study visit and less than the average income from 1990–2005. [Circulation 2019;doi:10.1161/CIRCULATIONAHA.118.035521]
Participants were also divided into tertiles of income volatility, defined as the intraindividual standard deviation (SD) of the percent change in inflation-adjusted income from 1990–2005: low (SD 0–21 percent change; n=1,303), medium (SD 22–51 percent change; n=1,306) and high (SD 52–242 percent change; n=1,304) variability.
Over the 10-year period from 2005–2015, 106 incident CVD events and 164 deaths were recorded. The corresponding incidence rates (IR) were 2.76 and 3.66 per 1,000 patient-year at risk.
CVD events occurred with much higher frequencies in participants with greater income variability. For instance, the IRs in the high and low variability tertiles were 4.37 and 1.70 per 1,000 patient-years, respectively, yielding a significant IR difference (2.66 per 1,000 patient-years; 95 percent CI, 1.31–4.02).
A similar trend was observed for all-cause mortality. The obtained IRs for the high vs low income variability tertiles were 5.28 and 2.12 per 1,000 patient-years, respectively, such that the IR difference also attained significance (3.16 per 1,000 person-years; 1.77–4.54).
Fully adjusted Cox proportional hazards models further confirmed these findings. The likelihood of CVD (hazard ratio [HR], 2.07; 1.10–3.90) and all-cause mortality (HR, 1.78; 1.03–3.09) was significantly elevated in the high vs low tertiles of income variability.
Drops in income also had a significant impact on CVD and all-cause mortality. The resulting IR differences were 4.46 and 5.61 per 1,000 patient-years in young adults with ≥2 relative to no income drop events. Associated risks were similarly significant (CVD: HR, 2.54; 1.24–5.19; all-cause mortality: HR, 1.92; 1.07–3.44).
“It is likely that there are specific psychosocial and biological pathways through which income volatility is associated with CVD and premature mortality,” said researchers.
For instance, it has previously been shown that earning low income is associated with unhealthy lifestyle behaviour such as alcohol consumption, smoking and engaging in low levels of physical activity. Stress also appears to play a central role, having been connected to inflammation and spikes in blood pressure. [Health Aff (Millwood) 2002;21:31-46; Soc Sci Med 2016;150:221-230; Circulation 2004;110:e554-e559]
However, these studies insufficiently elucidate the causal links between income status and adverse health outcomes. “Future studies focused on understanding mechanisms underlying the association between income volatility with CVD and mortality are warranted,” researchers added.