Inactivity May Cause More Heart Disease Than Smoking

Laird Harrison

May 09, 2014

Physical inactivity ranks higher than smoking, obesity, or high blood pressure among the causes of heart disease in Australian women older than 30 years, a new study shows.

"Programmes for the promotion and maintenance of physical activity deserve to be a much higher public health priority for women than they are now, across the adult lifespan," write Wendy J. Brown, PhD, from the Centre for Research on Exercise, Physical Activity and Health, School of Human Movement Studies, University of Queensland, St. Lucia, Australia, and colleagues.

The study was published online May 8 in the British Journal of Sports Medicine.

A previous study of the top 10 risk factors for disease worldwide put high blood pressure at the top, followed by smoking and air pollution from solid fuels.

However, Dr. Brown and colleagues hypothesize that circumstances are different in Australia than in other parts of the world. For example, Australians do not burn much solid fuel. The authors also thought risk factors might change with a woman's age.

Therefore, they set out to quantify the changing contribution made to a woman's likelihood of developing heart disease across her lifetime for each of the known top 4 risk factors in Australia: excess weight, smoking, high blood pressure, and physical inactivity.

They calculated the population-attributable risk, a mathematical formula used to define the proportion of disease in a defined population that would disappear if exposure to a specific risk factor were to be eliminated.

They based their calculations on estimates of the prevalence of the 4 risk factors among 32,154 participants in the Australian Longitudinal Study on Women's Health, which has been tracking the long-term health of women born in 1921-1926, 1946-1951, and 1973-1978 since 1996.

They found that the prevalence of smoking was highest among women aged 22 to 27 years, at 28%, and lowest in those aged 73 to 78 years, at 5%. However, the prevalence of inactivity and high blood pressure increased steadily across the lifespan from age 22 to 90 years, rising from 48% to 81% for inactivity and from less than 5% to 47% for hypertension.

Overweight increase was lowest, at 46%, in the youngest women (aged 22 - 27 years); peaked in middle age, at 79.2% in women aged 59 to 64 years; and then declined again in older age to 62.4% in women aged 85 to 90 years.

The researchers also used estimates of relative risk from the Global Burden of Disease study and applied them to the Australian women. Relative risk data indicate the likelihood that a woman with a particular risk factor will develop heart disease compared with someone without that risk factor.

Combining the prevalence and relative risk data, the researchers found that up to the age of 30 years, smoking was the most important contributor to heart disease, with a population-attributable risk of 59%, but its contribution to heart disease declined to 5.3% in women aged 73 to 78 years.

In contrast, "low" and "no" physical activity accounted for 47.2% of heart disease in women aged 22 to 27 years, rising to 50.9% in women aged 31 to 36 years and then gradually declining to 23.5% in women aged 85 to 90 years.

In contrast, the largest proportion of risk attributable to high body mass is 32.7% in women aged 31 to 36 years, and to hypertension is 10.7% in women aged 56 to 64 years.

The researchers estimate that if every Australian woman between the ages of 30 and 90 years were able to reach the recommended weekly exercise quota of 150 minutes of at least moderate intensity physical activity, then the lives of more than 2000 middle-aged and older women could be saved each year.

The authors also conclude that the contribution of different risk factors to the likelihood of developing heart disease changes across the lifespan.

Continuing efforts to curb smoking among the young are warranted, they say, but much more emphasis should be placed on physical inactivity, which, they say, has been dwarfed by the current focus on overweight and obesity.

The authors have disclosed no relevant financial interests.

Br J Sports Med. Published online May 8, 2014. Abstract

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