Based on data from the Women’s Health Study (WHS), Weinstein and colleagues used ‘hazard ratios’ to examine the impact of weight and exercise on the occurrence of heart disease over an average 11 years of follow-up. Hazard ratios are a tool that approximates ‘relative risk,’ which compares risk against a baseline rate. A ratio of ‘2’ implies the risk is doubled. In this instance, the baseline comparator was made up of non-overweight active women.
Over 38,000 women were followed and just under a 1000 were known to have developed a heart attack, need heart surgery or other procedure or have a stroke. Other concurrent conditions, like high blood pressure and diabetes were statistically accounted for/'neutralized.'
While being overweight (a BMI between 25 and 29.99) and inactive increased the hazard ratio (risk) by about 1.9 (i.e., almost doubled compared to being thin and active), being overweight and active had a hazard ratio that was less at 1.5 (the risk increased by 50%). Being obese (a BMI of 30 or greater) and inactive had a hazard ratio of 2.5, which decreased to 1.9 when women were active. Never mind the thin/active comparator. For both categories of overweight and obesity, going from active from inactive appeared to decrease the risk of heart attack, heart surgery and stroke by about 20% (and for the methodologists out there, that’s assuming there are no confounding variables and that the association is causal - and BTW that the differences are statistically significant).
But wait - it gets better. The authors described physical activity not in terms of formal ‘exercise’ but in terms of time spent walking; it appeared 30 minutes a day conferred protection.
So, based on this study, doctors, disease management programs, health educators, registered dietitians and other professionals can tell their women patients who are struggling with weight to be of good cheer: relatively modest levels of exercise are associated with a 20% improvement in the risk versus being inactive. The bad news is that overweight and obese women can’t exercise their way down the same level of cardiovascular risk as a thin active woman.
But it’s not even that bad. Note the data above were casted in terms of hazard ratios. A better question is what is the absolute risk? It’s not apparent in the Archives article above, but the DCMB had little trouble finding the answer in data from the Framingham Study. Having a BMI from 25 to 29.9 has a total yearly cardiac risk of 1.9 per thousand per year in women, while the risk among the obese is 2.4 per thousand per year. In other words the risks are 0.19% and 0.24% per year. The DMCB suspects that while being overweight/obese can ’double’ the risk versus thin persons, that doubling is at the margins. In other words, obese and overweight women have a 99% chance of NOT having a cardiovascular problem from year to year - with or without exercising.
This study is better thought of in these terms: if you are a woman with a high BMI, your less than 1% per year risk of heart attack and stroke may be decreased by a fifth if you walk 30 minutes a day. Doesn’t that sound better?
And finally, if you took the time to read that preceding 1000 word soliloquy-post on 'risk versus retail' (I apologize to readers about that, the DMCB got carried away), the above obesity numbers might lend some insight on why health insurers have been reluctant to include obesity programs as a covered benefit. Absent diabetes or heart disease (where the risk is considerable and weight loss can make a big difference in chronic disease control), obesity alone is probably not a big source of risk for the underwriters. They probably believe reducing the prevalence of obesity is unlikely to make a big difference in claims expense. Better to let it go retail.
Post script: we in the U.S. are not alone.
Post post script: slightly off topic, but while the DMCB agrees obesity is leading to epidemic levels of diabetes, hypertension and heart disease, it recalls seeing many otherwise well if chunky patients who were seeking 'treatment' because of how their girth appeared. Maybe the anti-fat bias activists have a point: our perception of health (as well as beauty) is also becoming distorted.