• obesity
• hypertension

Obesity represents one of the cardiovascular challenges of the twenty-first century.1 2 Obesity is a potent risk factor for the development of hypertension, diabetes and hyperlipidaemia, crucial for the subsequent development of cardiovascular disease.1 2 A greater understanding of the relationship between the timing of the onset of obesity and the development of these risk factors is of importance as it would allow for the tailoring of preventative strategies in populations at the highest risk.

Prior studies have documented the relationship between the development of obesity in early adulthood and the subsequent risk of hypertension. In an analysis of the Johns Hopkins Precursors Study, development of obesity (body mass index (BMI) ≥30 kg/m²) in young adulthood was associated with an increased risk of subsequent hypertension (HR 4.17, 95% CI 2.34 to 7.42), while overweight was also associated with an attenuated, yet significantly elevated risk (HR1.58, 95% CI 1.28 to 1.96).3 Further, in an analysis of the Nurses’ Health Study and Physicians’ Health Study, obesity in early adulthood was associated with an increased risk of hypertension in middle adulthood in both men (incident rate ratio (IRR) 1.21, 95% CI 1.12 to 1.31) and women (1.24, 95% CI 1.20 to 1.28) in multivariable adjusted models.4 A similar relationship between stable obesity in early adulthood and subsequent hypertension has been observed in a study using data from the National Health and Nutrition Examination Survey.5 Less well understood, however, is whether there is a specific age of onset of overweight or obesity that portends a higher risk of subsequent hypertension.

In this issue of the journal, Li et al 6 make an important contribution to the field by examining the relationship between the age of onset of overweight or obesity and subsequent hypertension. The authors examined a cohort of patients free of hypertension at baseline from the Kailuan Study, an occupational cohort of employees from a coal mine company based on Tangchan, China. Using the standard WHO definition,1 a total of 4742 patients with new-onset overweight or obesity were compared with an age-matched and sex-matched group of 4742 patients with normal BMI using Cox models and the Fine and Grey method to account for the competing risk of death. During a mean follow-up of 5.17 years, a total of 1642 (34.6%) overweight and 1293 (27.3%) normal-weight participants developed subsequent hypertension. Multivariable adjustment for confounders was performed. Age of onset of overweight or obesity at 18–39 years, 40–49 years, 50–59 years was associated with a modest but significant risk of hypertension, while age ≥60 years was not. The youngest cohort appeared to have the highest risk (HR 1.38, 95% CI 1.11 to 1.72), with a linear decrease in the risk of new-onset hypertension with increasing age of onset of obesity (40–49 years: HR 1.27, 95% CI 1.09 to 1.49, 50–59 years: HR 1.22, 95% CI 1.09 to 1.40, and ≥60 years: HR 1.14, 95% CI 0.99 to 1.32). The study results remained robust when patients who developed overweight but who subsequently returned to normal weight during follow-up were excluded from the analysis, and when the WHO International Obesity Task Force definition for overweight and obesity in east Asian populations was used.7

Strengths of the paper include the large sample size, the regular, longitudinal follow-up, the availability of serial measurement of participants’ weights during the study, and the robustness of the results after sensitivity analyses. The study also has important limitations. First, the vast majority of patients was deemed to have developed hypertension if they had a single blood pressure measurement of ≥140/90 mm Hg during follow-up. International guidelines’ definition of hypertension require multiple readings greater than 140/90 mm Hg at different occasions to define hypertension, and it is likely that hypertension was overestimated in this study.8 Second, the study population primarily consisted of men and thus it was underpowered to examine effect modification by sex. Third, the study population consisted of a Chinese occupational cohort, and thus the results may not be generalisable to broader populations or other ethnicities. Finally, the study was not able to examine the effects of age of onset of overweight downstream of hypertension, such as its effect on the onset of cardiovascular disease or adverse cardiovascular outcomes.

In conclusion, the study of Li et al contributes to our understanding of the relationship between age of onset of overweight and obesity and the subsequent development of hypertension. Onset of overweight in younger adulthood was associated with a greater risk of incident hypertension. These data suggest that prevention efforts aimed at the reduction or delay of overweight and obesity in younger individuals, may significantly impact the onset of hypertension in later life. Whether such an intervention significantly impacts the onset of cardiovascular disease and its related adverse outcomes requires future study.