Hypertension, or increased blood pressure, is one of the more important ways in which the low-level molecular damage of aging is converted into high-level structural damage to tissues. Hypertension produces increased rupture of capillaries and other forms of pressure damage to delicate structures of the brain and other organs, resulting in loss of function and, ultimately, death. It also accelerates the progression of atherosclerosis, the creation of fatty plaques that weaken and narrow blood vessels, with the end result of stroke or heart attack as an important blood vessel suffers structural failure.
Being overweight or obese is strongly associated with risk and degree of hypertension. The underlying mechanisms are easy to speculate on: the chronic inflammation produced by visceral fat tissue causes dysfunction in the smooth muscle cells that control blood vessel dilation and constriction, for example. That breaks the feedback mechanisms controlling blood pressure, leading to hypertension. The diet needed to become overweight likely contributes to greater cross-link formation, stiffening blood vessel tissues to produce much the same outcome. And so forth through a laundry list of other low-level damage that manifests in blood vessel walls.
Among the cardiovascular disease (CVD) risk factors, age is considered as the most important predictor of CVD events and hypertension is a major cause of CVD mortality. Age-related increase in blood pressure (BP) is recognized as a universal feature of human aging. Previous epidemiological surveys have shown a progressive increase in systolic blood pressure (SBP) with age, whereas diastolic blood pressure (DBP) also initially increases with age but falls at latter ages. Thus, effective control of BP is essential for improving population health.
Studies of BP associated with adiposity-related genetic variants and controlled trials of weight loss interventions have established the causal relationship between adiposity and BP. Regardless of age and other unmodifiable CVD risk factors such as sex and race, there are many risk factors that are manageable and can be controlled through lifestyle modification, including reduction of obesity. However, there are inconsistencies as to whether a general or central adiposity is more strongly associated with BP and different opinions about which variable is the strongest predictor of BP.
The present study aimed to investigate how BP and body composition change within different age groups and their correlation across the adult age span. We also investigated the contribution of body composition measures (including body mass index (BMI), lean mass percent (LM%), and visceral fat rating (VFR) to the age-related alteration of BP across ten 5-year age groups ranging from 18-79 years in a sample of healthy Chinese adults. We demonstrated that mean SBP showed an age-related increase and mean DBP showed an inverted U-shape across the age span, and this trend was closely associated with the age-related body composition changes. Furthermore, we found that the association between BP and body composition indices was weaker in the elderly compared to the younger subjects.
As demonstrated in our study, all measures of general obesity, central obesity, and LM% were correlated to BP at the whole population level, and among them the relationships with BP were similar across most of the body composition indices. Some studies have suggested that general adiposity was more strongly correlated with BP, while other studies suggested central or visceral adiposity was more strongly correlated with BP than general adiposity. In this study, we didn't find significant differences between these two kinds of obesity indices.
To examine whether body composition was a factor influencing BP throughout the whole adult age span, we further analyzed the association of BP with BMI, LM% and VFR in each specific age-group (at 5-year ranges). After adjustment for education level, smoking status, alcohol consumption, and residential location, BMI and VFR were positively associated with BP in each age group, suggesting that adiposity was an important risk factor for the increased BP, whereas LM% was negatively associated with BP, the latter indicating its protective effect on BP. The correlation between BP and all these three measures (BMI, LM%, and VFR) was weaker in the elderly than younger adults. Thus, as demonstrated by our study, we may infer that factors associated with increased BP may be more complicated in the elderly compared to the younger age groups.