Skip navigation

Being unfit: as life threatening as other risk factors

 

Many articles have examined the association between physical inactivity and death. The aim of this study is twofold: (i) to quantify this association; and (ii) to quantify associations between physical inactivity and other risk factors. The intention is to compare the effect of being unfit, with other factors, on the risk of death from cardiovascular disease and all-causes in normal-weight, overweight and obese men.

Bottom line

Low fitness is as important as diabetes, cholesterol level, hypertension and smoking on the risk of death from cardiovascular disease and all-causes in normal-weight, overweight and obese men.

Reference

M Wei et al. Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men. Journal of the American Medical Association 1999 282: 1547-1553.

Study

Participants were 25,714 men, with an average age of 43.8 years, from the Aerobics Center Longitudinal Study. This was a US study of patients who attended a preventive medicine clinic for health checks. Participants received a medical examination during 1970 to 1993, with follow-up until 1994. Length of follow-up was therefore between one and ten years. Excluded were patients with a history of cancer, those with a body mass index of less than 18.5 kg/m2, those younger than 20 years of age and those with less than one year of follow-up.

Patients completed questionnaires on demographics, personal and family health history and health habits (including smoking and physical activity). The physical examination included measurements of height, weight, blood pressure, lipid and fasting plasma glucose levels.

Men were classified as normal weight (body mass index 18.5 to 24.9 kg/m2), overweight (body mass index 25.0 to 29.9 kg/m2) or obese (body mass index 30.0 kg/m2 or more).

The presence or absence of the following six risk factors was established:

  1. cardiovascular disease (definition included previous myocardial infarction, stroke, myocardial revascularisation, abnormal electrocardiogram);
  2. type 2 diabetes mellitus (defined as history of physician-diagnosed type 2 diabetes mellitus or fasting plasma glucose levels of at least 7.0 mmol/L);
  3. high serum cholesterol level (defined as serum cholesterol higher than 6.2 mmol/L);
  4. hypertension (defined as history of physician-diagnosed hypertension or blood pressure of at least 140/90 mm Hg);
  5. current smoking;
  6. low cardiorespiratory fitness (assessed with a maximal exercise test on a treadmill).

Mortality was established through the National Death Index and cause of death by coding death certificates according to the International Classification of Diseases, Ninth Revision.

Results

More than 95% of participants were white. Of the 25,714 participants: 10,623 (41%) were normal weight, 367 died, 126 from cardiovascular disease; 11,798 (46%) were overweight, 500 died, 237 from cardiovascular disease; and 3293 (13%) were obese, 158 died, 76 from cardiovascular disease. As body mass index increased from normal to obese, so did the prevalence of baseline cardiovascular disease, family history of cardiovascular disease, diabetes mellitus and hypertension. Compared with normal-weight men, overweight and obese men were more likely to smoke, be sedentary, have higher blood pressure and raised cholesterol and triglyceride levels.

Tables 1 and 2 show the risk of death from cardiovascular disease and all-causes by body mass index and six other risk factors (adjusted for age and examination year). The reference groups were normal weight men (for the overweight and obese) who did not have the specific risk factor.

Table 1. Relative risk of cardiovascular death (comparison groups are normal weight men, for the overweight and obese, without the specific risk factor).

Risk factor

Normal weight

Overweight

Obese

Cardiovascular disease

6.9

8.1

14

Type 2 diabetes mellitus

2.2

3.9

4.9

Cholesterol level above 6.2 mmol/L

1.4

2.8

4.7

Hypertension

2.6

3.4

4.5

Current smoker

2.1

3.3

4.4

Low fitness

3.1

4.5

5.0

Table 2. Relative risk of all-cause death (comparison groups are normal weight men, for the overweight and obese, without the specific risk factor).

Risk factor

Normal weight

Overweight

Obese

Cardiovascular disease

2.7

3.0

4.7

Type 2 diabetes mellitus

1.5

2.4

3.1

Cholesterol level above 6.2 mmol/L

1.1

1.7

2.7

Hypertension

1.6

1.9

2.3

Current smoker

1.7

2.1

3.0

Low fitness

2.2

2.5

3.1

For each risk factor, as body mass index increased, risk of death increased. The strongest predictor of death was cardiovascular disease. Overweight men with any of the other risk factors were approximately three to four times more likely to die from cardiovascular disease and twice as likely to die from all-causes than normal-weight men without the condition. Obese men with any of the other risk factors were approximately five times more likely to die from cardiovascular disease and three times more likely to die from all-causes than normal-weight men without the condition.

Table 3 shows the population attributable risks for cardiovascular and all-cause mortality, i.e. the estimated percentage of the population who died from each risk factor, according to body mass index. The results were adjusted for age, examination year, parental history of cardiovascular disease and all the other risk factors. The comparison groups were men within each body mass index range who did not have the risk factor.

Table 3. Estimated percentage of the population who died from each risk factor according to body mass index.

Risk factor

Normal weight

Overweight

Obese

 

CVD

All-cause

CVD

All-cause

CVD

All-cause

Cardiovascular disease

45

19

38

19

51

27

Type 2 diabetes mellitus

5

2

8

6

15

9

Cholesterol level above 6.2 mmol/L

5

0

16

8

26

18

Hypertension

26

12

13

13

15

4

Current smoker

11

7

10

9

6

9

Low fitness

15

10

25

18

39

44

 

Comment

On an individual level, cardiovascular disease was the strongest predictor of death. Low fitness was comparable with diabetes, high cholesterol, hypertension and smoking as a predictor of mortality.


From a population perspective, cardiovascular disease carried the highest risk of death in normal-weight men, and cardiovascular disease and low fitness were comparable risks in overweight and obese men. To be more specific, 27% of obese men died of all-causes because of cardiovascular disease and 44% died because they were unfit. These figures show the huge importance of physical activity. Furthermore, physical activity effects the other risk factors: it reduces the risk of cardiovascular disease, diabetes and hypertension and lowers cholesterol levels. All in all, a powerful article.