Start Slim, Stay Slim, Live Longer

November 15, 2013

By Will Boggs, MD

NEW YORK (Reuters Health) Nov 15 - Maintaining a healthy weight from young adulthood through middle age helps people live longer, a new study shows.

Excess weight in young adulthood or middle age, however, is associated with mortality, the researchers say.

In the NIH-AARP Diet and Health Study, people who entered adulthood with a low body mass index (BMI), avoided gaining weight, and maintained a healthy BMI throughout adulthood lived longer than those who started out overweight, became overweight, or stayed overweight.

"Our study found that both overweight and weight gain in younger to middle adulthood (18 to 50 years in our study) is strongly related to mortality later in life," Dr. Kenneth F. Adams from Minnesota Cancer Surveillance System in St. Paul told Reuters Health. "To reduce mortality in their patient populations, physicians should strongly encourage their younger patients to maintain a normal, stable weight."

Previous studies have shown that BMI at younger ages more strongly predicts mortality than BMI at older ages does, and several studies have indicated that weight gain is unrelated to or only equivocally associated with mortality.

"Most previous research has failed to find a relationship between weight gain and mortality," Dr. Adams said. "But it doesn't make sense that body mass index would be associated with mortality- which it is, and weight gain would not. We resolved the paradox by evaluating adult weight over three specific age intervals."

The NIH-AARP Diet and Health Study included 109,947 men and women aged 50 to 71 years at entry in 1995-1996.

Compared with the lean group (BMI 18.5-22.4), individuals whose BMI at age 18 was in any higher group faced significantly greater risk of mortality. In fact, the hazard ratio associations with all higher BMI groups were strongest at age 18 and declined somewhat with age.

The associations of elevated BMI with mortality were strongest for cardiovascular disease-related deaths. Mildly elevated BMI (25.0-27.4) at age 18 increased the risk by 65%, and BMI of 27.5 or more increased the risk of cardiovascular disease-associated mortality by 2.42-fold, the authors reported online October 29th in the American Journal of Epidemiology.

Weight gain between ages18 and 35 and between 35 and 50 was also strongly associated with mortality, whereas mild weight gain between 50 and 69 years slightly decreased the risk of mortality. In the latter age group, even gains of more than 1 kg per year only slightly increased the mortality risk (by 17%).

The relationship between weight gain and increased mortality risk was significant only among individuals reporting very good to excellent health.

In the 18 to 35 interval, the highest mortality risk occurred among individuals with an initial BMI of 25.0 or more (at age 18) who gained more than 1 kg/year by age 35. Mortality risk was intermediate in participants who either had an initially normal BMI but gained weight over the interval or who had an initially high BMI but did not gain weight.

Associations between initial BMI and BMI change and mortality were weaker in the 50 to 69 age interval. In this group, weight gain of 1 kg/year or less was not associated with increased mortality risk. Weight loss in this interval was associated with greater risk of mortality regardless of health status.

"The relationship between body weight and health status in older adults is complicated," Dr. Adams said. "Our study could not distinguish between intentional and unintentional weight loss, so we were not in a position to evaluate whether intentional weight loss is beneficial. But overall, weight loss was associated with increased mortality. To me, this suggests that physicians should focus their preventive strategies for this population on interventions other than weight loss."

Dr. Margaret Allman-Farinelli from the University of Sydney, New South Wales, Australia wrote a commentary that was published with the report. She told Reuters Health by email, "In the younger adults, there is a good chance of preventing weight gain and the spill over into overweight and obesity and it is my belief prevention is better than cure."

"Weigh your patients and be alert to persistent weight gain," Dr. Allman-Farinelli advises. "A young adult with BMI 24 may seem fine to you but if within the year they gain two or three pounds and again the next year you should be acting on this. By the time a patient is overtly obese it will be very difficult to reverse the situation. An already obese young adult warrants specialist counseling from a dietitian or perhaps psychologist or both."

Dr. Allman-Farinelli added, "As well as taking height and weight a tape measure would be handy to measure waist circumference. It seems that it may (prove to be a) better predictor of metabolic disease than BMI."

Obesity researcher Dr. Ryan Masters from University of Colorado in Boulder told Reuters Health by email, "The size of the BMI-mortality associations reported by Adams et al. are substantively larger than those commonly reported. But recent work that is attentive to (1) age, (2) cohort, and/or (3) duration of high BMI all find results consistent with a stronger BMI-mortality association that persists across all ages."

"Weight gain has not been uniform in the US population," he added. "Different cohorts have different prevalence of obesity, and differ in terms of the ages at which the increases occur."

"In short," he continued, "recent birth cohorts are at an increased risk of early death relative to the rest of the population because they have higher rates of obesity earlier in their life courses, and thus live their lives with high BMI levels for much longer periods of time than older cohorts."

"Adams et al.'s work clearly shows that the earlier one becomes obese in their life courses, the greater the risk of early death," Dr. Masters concluded. "I think the authors do well to emphasize the importance of intervening early in life."

SOURCE: http://bit.ly/1hM1glB

Am J Epidemiol 2013.

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