Gajalakshmi V, et al. - Researchers determined the associations between body-mass index (BMI), systolic blood pressure, and mortality in an Indian South Asian population. They observed little association of BMI with vascular mortality, even though increased BMI was found to be related to increased systolic blood pressure, which ultimately has a link to increased vascular mortality. These data suggested important adverse effects of some close correlates of below-average BMI, which could be of relevance in all populations.

Methods

• Researchers performed a prospective study including men and women aged 35 years or older from the general population in Chennai, India between January 1, 1998 and December 31, 2001.
• Participants were interviewed to obtain information regarding age, sex, education, socioeconomic status, medical history, tobacco smoking, alcohol; measurements of height, weight, and blood pressure were also recorded.
• They identified deaths via Chennai city mortality records and with the help of trained graduate non-medical fieldworkers who visited households.
• Following the baseline survey, visits to households were performed once in 2002–2005, then biennially until 2015.
• During these repeat visits, they recorded structured narratives of any deaths that took place before March 31, 2015 for physician coding.
• They evaluated long-term variability in systolic blood pressure and BMI by resurveying a random sample of participants as per baseline during 2013-2014.
• They used Cox regression (standardized for tobacco, alcohol, and social factors) to relate mortality rate ratios (RRs) at ages 35-69 years to systolic blood pressure, BMI, or BMI adjusted for usual systolic blood pressure.

Results

• For this study, a total of 500,810 participants were recruited.
• A total of 414,746 participants aged 35-69 years (mean 46 [SD 9]; 45% women) remained after excluding those with chronic disease or incomplete data.
• Mean systolic blood pressure was 127 mm Hg (SD 15), and mean BMI was 23.2 kg/m² (SD 3.8) when measured at recruitment.
• The observed correlations of resurvey and baseline measurements were 0.50 for systolic blood pressure and 0.88 for BMI.
• Findings demonstrated a strong association of low BMI with poverty, tobacco, and alcohol.
• They reported 29,519 deaths at ages 35-69 years; 14,935 of these were attributed to vascular cause (12,504 cardiac, 1881 stroke, and 550 other).
• A strong association of vascular mortality with systolic blood pressure was observed: RRs per 20 mm Hg increase in usual systolic blood pressure were 2.45 (95% CI 2.16–2.78) for stroke mortality, 1.74 (1.64–1.84) for cardiac mortality, and 1.84 (1.75–1.94) for all vascular mortality.
• They noted a strong impact of BMI on systolic blood pressure (an increase of about 1 mm Hg per kg/m²) and diabetes prevalence, however, BMI showed little association with cardiac or stroke mortality, with only small excesses even for grade 1 obesity (ie, BMIs of 30.0–35.0 kg/m²).
• An inverse association of BMI with cardiac and stroke mortality was evident throughout the range 15.0–30.0 kg/m² after additional adjustment for usual systolic blood pressure: comparison of underweight participants (ie, BMI 15.0–18.5 kg/m²) with overweight participants (ie, BMI 25.0–30.0 kg/m²) revealed the blood-pressure-adjusted RR to be 1.28 (95% CI 1.20–1.38) for cardiac mortality and 1.46 (1.22–1.73) for stroke mortality.