April 2, 2014

Seniors Who Pack Some Extra Pounds May Live Longer

Here’s some news I was happy to see: people 65 and older may actually live longer if they carry some extra weight, as I do.

For years, people have been considered “overweight” -- according to the World Health Organization (WHO) – if their Body Mass Index (BMI) falls between 25 and 30. Anything over 30 is considered obese.

Without making you feel you’re back in algebra class, BMI equals your weight in kilograms divided by the square of your height in meters (BMI = kg/m2). The U.S. Department of Health and Human Services makes it a little easier for those of us who don't use the metric system and don't fancy doing arithmetic. Here's NIH's BMI calculator. All you need to do is plug in your height (feet and inches) and weight (pounds).

Researchers at Deakin University in Melbourne, Australia, collected and then re-evaluated data from studies published between 1990 and 2013 that had analyzed links between BMI and mortality in people 65 and older. They tracked that correlation for over 200,000 seniors over an average span of 12 years.

In the March issue of the American Journal of Clinical Nutrition, Deakin and her team published their findings about seniors and BMI. Among their conclusions:
  • If BMI fell between 23.0 and 23.9 – on the high side of the WHO’s “overweight” category – there was no increased risk of death.
  • If BMI fell between 21 and 22 – in the “normal” range, there was a 12% increase in death risk.
  • If BMI fell between 20 and 20.9 – on the lower end of “normal” – there was a 19% increase in death risk.
  • By contrast, if BMI fells between 33 and 33.9 – on the high side of “obese” – there was (only) an 8% increase in death risk.
Time to Re-Assess the WHO's Recommended BMI for Seniors?
The numbers suggest that the WHO’s BMI guidelines for seniors should be adjusted, just as medical experts have recently adjusted blood pressure guidelines for seniors (150/90 is now considered the high end of OK, a significant change from the long-held 120/80).

Study leader Caryl Nowson, professor of nutrition and aging at Deakin University, summed it up this way: “Our results showed that those over the age of 65 with a BMI of between 23 and 33 lived longer, indicating that the ideal body weight for older people is significantly higher than the recommended 18.5-25 'normal' healthy weight range."

In addition to suggesting a WHO reassessment of healthy body weight for seniors, she also cautions: "Factors such as chronic diseases and the ability to move around need to be considered as there is no real issue with being in the overweight range unless it is preventing people from moving around freely."

One More Time: Diet and Exercise
She urges seniors to ditch the weight loss programs and concentrate instead on getting a balanced diet and staying active. Once again, it comes down to those reliable old standbys: diet and exercise.

Nowson also cautions that seniors risk malnutrition when they rigorously observe certain dietary restrictions: "Malnutrition in older people is not well recognised as this can occur even when BMI is in the overweight range.”

Critics of the standard BMI measurements say the formula doesn't account for other important factors, like age, and muscle-to-fat ratio. An article in Medical News Today highlights several other concerns about using BMI to evaluate health:
What is the problem with BMI?
BMI is a very simple measurement which does not take into account the person's waist, chest or hip measurements. An Olympic 100 meters sprint champion may have a BMI higher than a couch potato of the same height. The couch potato may have a big belly, not much muscle and a lot of body fat on his hips, upper thighs, in his blood and other parts of his body. While the athlete will have a smaller waist, much less body fat, and most likely enjoy better health. According to a purely BMI criteria, the couch potato is healthier.
BMI does not take into account bone density (bone mass). A person with severe osteoporosis (very low bone density) may have a lower BMI than somebody else of the same height who is healthy, but the person with osteoporosis will have a larger waist, more body fat and weak bones.
Many experts criticize BMI as not generally useful in evaluation of health. It is at best a rough ballpark basic standard that may indicate population variations, but should not be used for individuals in health care.
Put simply: experts say that BMI underestimates the amount of body fat in overweight/obese people and overestimates it in lean or muscular people. 
More information on BMI, together with imperial and metric BMI calculators, is available here
Nick Trefethen, a Professor of Numerical Analysis at Oxford University's Mathematical Institute, has created what he believes to be a better, more accurate and relevant formula for the BMI one for deciding whether people are carrying too much fat. Humans do not grow equally in all three dimensions, he explains - the existing BMI formula presumes we do.


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