How to Avoid a Heart Attack, Wherever You Live

Summarized by Robert W. Griffith, MD
September 26, 2005

Introduction

You've heard it before, but it bears repeating, along with supportive evidence. It is possible to ward off a heart attack if you address the known risk factors early enough. And that's not just the case for people living in developed countries. A study conducted in 52 countries has established the worldwide risk factors, based on information from 30,000 men and women. It also looked for what they called 'population attributable risks' (PAR); for instance, serum cholesterol levels might be lower in Chinese people. Results have been reported in the medical journal Lancet, and we summarize the main findings here.

What was done

The 52 countries were located in Asia, Europe, the Middle East, Africa, Australia, North America, and South America. There were 262 study centers, which were selected based on the feasibility of being able to conduct the study there.

All patients admitted to coronary care units (or their local equivalent) were screened for a first-time heart attack (myocardial infarction, or MI). As controls, at least one age- and gender-matched person without a heart attack was recruited, either from the same hospital or from the local population. About 2/3 of the controls were hospital patients, and 1/3 were from the community - attendants or relatives from a non-cardiac patient. This approach is what is known as a case-control study.

Questionnaires and physical exams were done in the same way in both cases and controls, in all centers. Age, gender, economic and educational status, lifestyle (smoking, physical activity, nutrition), family history of heart disease, high blood pressure, diabetes, and symptoms of depression or stress were recorded. Physical examination included height, weight, waist and hip measurements, fasting blood sugar, blood lipid levels, and ApoB/ApoA1 ratios. (This last test, which has been shown to be predictive of MI, is another way of expressing a high or a low HDL-cholesterol to LDL-cholesterol ratio. It can be measured in non-fasting plasma, a clear advantage in clinical practice.)

Statistical analyses made appropriate adjustments from region to region for differences in ages of the different populations. Then, estimates were made of odds ratios (the likelihood of having an MI) were calculated for the different risk factors, and analyzed for each of different regions.

What was found

There were over 15,000 MI cases and 14,800 controls enrolled over a 4-year period. After elimination of those who had insufficient or clearly wrong data, there were 12,461 cases and 14,637 controls included in the analyses.

The average age at the time of a first MI was 9 years earlier in men than in women. An alarming finding was that more than 10% of men with an MI in the Middle East, Africa, and South Asia were below 40 years of age; this suggests a looming epidemic in these regions.

The odds ratios for the risk factors analyzed are given in the table below:

Risk Factor	Odds Ratio	Regional Risks?
Raised ApoB/ApoA1	3.25	World-wide
Smoking	2.87	World-wide
Stress/Depression	2.67	World-wide
Diabetes	2.37	SE Asia, Africa, Middle East
Hypertension	1.91	SE Asia, S America, Africa
Raised Waist/Hip Ratio	1.62	Europe, N America, Australia, NZ, SE Asia
Regular Alcohol Use	0.91	SE Asia, Africa, N America
Physical Activity	0.86	Europe, SE Asia, Americas
Eating Fruits & Veggies	0.70	N America, SE Asia, China

The presence of the first six factors all increased the likelihood of an MI, whereas undertaking the last three reduced the risk off an MI. Although there were measurable regional differences in the importance of the last 6 factors, the odds ratios given in the table are for the full global analysis.

Use of the waist-to-hip ratio, rather than body mass index (BMI), is the simplest estimate of the abdominal fat associated with diabetes and atherosclerosis. It proved to be a better predictor of MI than BMI scores.

What these results tell us

It's been stated before that 50% of MIs occur in people without any warning or obvious risk factors. This is clearly false, as the results of this study show - there are 9 easily-measured and modifiable risk factors that account for over 90% of the risk of having a first MI. These factors are the same for men and women across different geographic regions throughout the world, and across different ethnic groups. The two most important risk factors are smoking and abnormal lipids, which together account for about two-thirds of the traceable risks. But the other 7 are also modifiable and well-worth undertaking.

While some areas in well-developed countries are well informed about the lifestyle to adapt to minimize coronary heart disease, the global aspect of this study, coupled with the earlier age of occurrence of first MIs in less developed parts of the world, point up the need for much better education in health matters, worldwide.

Source

• Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case-control study. S. Yusuf, S. Hawken, S. Ounpuu,  et al., Lancet, 2005, vol. 364, pp. 937--952

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