Increasing BMI Tracks With Hypertension Over a Lifetime
Steve Stiles, Nov 16, 2012
BALTIMORE, Maryland — New results from a study tracking medical students for almost 50 years shows that weight gain at any time in their lives increased their risk of developing hypertension . Dr Hasan M Shihab (Johns Hopkins University School of Medicine, Baltimore, MD) and colleagues report their findings online November 14, 2012 in Circulation. “We were able to track body-mass index [BMI] and blood pressure right from the age of about 22 up to age 65, and the big thing here is the length of follow-up, which was up to 49 years,” Shihab told heart wire. He noted that the longest follow-up period previously reported for this kind of analysis has been about 23 years.
Obesity in young adulthood conferred a threefold risk of hypertension, even after researchers accounted for lifestyle factors over the 50 years, compared with those who were normal weight, he and his colleagues report. And men who were of normal weight in early adulthood but became overweight or obese in midlife were twice as likely to develop hypertension as men who maintained a normal weight. Perhaps not surprisingly, those who stayed a normal weight were at the lowest risk of developing high blood pressure, the researchers say. “In the US we have a big problem of obesity, with two-thirds of adults being overweight or obese” and 32% of those aged 12 to 19 falling into the same category, says Shihab. “Our work shows how important it is to design ways to prevent obesity from developing in younger adults,” he observes. Prevention is so important because of the difficulty in maintaining weight loss, he adds: “If you lose weight, it’s always good, but being able to sustain it is the challenge.”
Participants Were Med Students, So Responses Should Be Reliable
The researchers studied the association of BMI with risk of developing hypertension in 1132 white men in the Johns Hopkins Precursors Study, which began enrollment in 1947. Prior research in this field has either suffered from short follow-up times, recall bias for ascertainment of BP, or no adjustment for potential confounders during follow-up or has been limited to a narrow age window not extending beyond middle age, Shihab and colleagues note. They concentrated on three time points for assessment: around the ages of 25, 45, and 65, although Shihab points out that the oldest participants were up to 85 years old. The fact that the participants became doctors means that their responses can be considered quite reliable, something that has been demonstrated in other studies, says Shihab. Other strengths include very high response rates, adjudication of hypertension diagnosis, and repeated measures of BP and lifestyle factors.
Over a median of 46 years of follow-up, 508 men developed hypertension. Obesity (BMI of >30 kg/m 2) in young adulthood was strongly associated with incident hypertension (hazard ratio 4.17). Overweight (BMI 25 to <30 kg/m 2) also signaled increased risk (HR 1.58). Men of normal weight aged 25 who became overweight or obese at age 45 were at increased risk compared with men of normal weight at both times (HR 1.57) but not men who were overweight or obese at 25 who returned to normal weight at age 45 (HR 0.91).
In addition, the rate of change in BMI over the life course increased the risk of incident hypertension in a dose-response fashion, with the highest risk among men with the greatest increase in BMI (HR 2.52).
“Few studies have examined the life course of BMI and risk of hypertension,” Shihab noted. And while he says the findings may not be generalizable to women, men of lower socioeconomic status, or ethnic minorities, “our long-term perspective shows how body weight influences risk even after accounting for lifestyle factors.”
Shihab HM, Meoni LA, Chu AY, et al. Body mass index and risk of incident hypertension over the life course: The Johns Hopkins Precursors Study. Circulation 2012; DOI: 10.1161/CIRCULATIONAHA.112.117333. Available at: http://circ.ahajournals.org. Abstract