Obesity as a risk factor in venous thromboembolism

Results 

The proportion of hospitalized patients diagnosed with obesity ranged from 1.4% to 2.4% over the 21-year period of observation. Among hospitalized patients diagnosed with obesity, 91000 of 12015000 (0.76%) had pulmonary embolism. Among hospitalized patients who were not diagnosed with obesity, pulmonary embolism was diagnosed in 2366000 of 691000000 (0.34%). Deep venous thrombosis was diagnosed in 243000 of 12015000 patients (2.02%) diagnosed with obesity and in 5524000 of 691000000 patients (0.80%) who were not diagnosed with obesity. The average ages of obese patients with pulmonary embolism (57 ± 17 years) (mean ± standard deviation) and deep venous thrombosis (55 ± 15 years) were lower than the average ages of non-obese patients with pulmonary embolism (64 ± 12 years) and deep venous thrombosis (61 ± 11 years).

The relative risk of deep venous thrombosis, comparing obese patients with non-obese patients, was 2.50 (95% CI = 2.49-2.51). The relative risk of pulmonary embolism was 2.21 (95% CI = 2.20-2.23). Obese females had a greater relative risk for deep venous thrombosis than obese males, 2.75 (95% CI = 2.74-2.76) versus 2.02 (95% CI = 2.01-2.04). Data were sufficient for comparison of the relative risk of pulmonary embolism according to age and sex only among patients aged 60 to 69 years and 70 to 79 years. For those aged 60 to 69 years, the relative risk for pulmonary embolism was 1.48 (95% CI = 1.45-1.50) in women and 1.27 (95% CI = 1.24-1.30) in men. For those aged 70 to 79 years, the relative risk for pulmonary embolism was 2.12 (95% CI = 2.09-2.16) in women and 1.90 (95% CI = 1.85-1.95) in men.

Obesity had the greatest impact on patients aged less than 40 years, in whom the relative risk for pulmonary embolism in obese patients was 5.19 (95% CI = 5.11-5.28) and the relative risk for deep venous thrombosis was 5.20 (95% CI = 5.15-5.25) (Table 1). In females aged less than 40 years, the relative risk for deep venous thrombosis comparing obese with non-obese patients was 6.10 (95% CI = 6.04-6.17). In males aged less than 40 years, the relative risk for deep venous thrombosis was 3.71 (95% CI = 3.64-3.79).

Table 1. Relative risks of pulmonary embolism and deep venous thrombosis according to age among obese and non-obese patients

	Age groups	Pulmonary embolism		Deep venous thrombosis
		Obese vs non-obese		Obese vs non-obese
		Relative risk	(95% CI)	Relative risk	(95% CI)
	<40 y	5.19	(5.11–5.28)	5.20	(5.15–5.25)
	40–49 y	1.94	(1.91–1.97)	2.13	(2.11–2.15)
	50–59 y	1.25	(1.23–1.27)	1.67	(1.65–1.68)
	60–69 y	1.42	(1.40–1.44)	1.88	(1.87–1.90)
	70–79 y	2.07	(2.04–2.10)	1.89	(1.87–1.91)
	>80 y	3.15	(3.08–3.22)	2.16	(2.12–2.20)
	All ages	2.18	(2.16–2.19)	2.50	(2.49–2.51)

CI = confidence interval.

Discussion 

These data show that obesity is a risk factor for pulmonary embolism and deep venous thrombosis in men as well as women. Obesity seems to be a stronger risk factor in women and in men and in women less than 40 years of age.

An advantage of the NHDS database is its extensive coverage of all races, ages, and regions of the United States. A disadvantage is that the basis for the diagnosis of obesity was not defined. Even so, the proportion of hospitalized patients diagnosed with obesity was within a narrow range over the period of observation, indicating consistency in the diagnostic process. Previous investigators used several indices of obesity including a body mass index (BMI) greater than 35 kg/m2, BMI 30 to 35 kg/m2,15 BMI greater than 30 kg/m2,7, 12 BMI greater than 29 kg/m2,6 weight more than 20% of median recommended weight for height,3 and waist circumference greater than 100 cm.10 The physicians’ assessment was accepted in 28% to 33% of patients reported by Anderson and associates.3, 4 It is likely that all patients with obesity diagnoses in the NHDS database were in fact obese, irrespective of the criteria used. However, some obese patients may not have had a listed discharge diagnosis of obesity, and they would have been included in the non-obese group. This would have tended to reduce the relative risk of obesity in venous thromboembolism. The somewhat younger ages of obese patients with pulmonary embolism and deep venous thrombosis, compared with non-obese patients, would have decreased the relative risk of obesity.

The relative risks for pulmonary embolism and deep venous thrombosis were similar to relative risks reported in smaller investigations that used defined criteria for obesity. In women with a BMI greater than 30 kg/m2, the relative risk for deep venous thrombosis, compared with non-obese women, was 2.4.8 In women with a BMI of 29 kg/m2 or more, the relative risk for pulmonary embolism was 2.9.6 In the Framingham Study, obesity was a risk factor only in women.7 Coon and Coller9 also showed that obesity was a risk factor only in women. Oral contraceptives in obese women increased the relative risk of deep venous thrombosis to 9.8.8 Men with a waist circumference of 100 cm or more had a relative risk of 3.9 for venous thromboembolism compared with men with smaller waists.10 Among men and women together, the risk ratio for deep venous thrombosis, comparing obese with non-obese patients, was 2.39.16 Some found that obesity was not an independent risk factor for venous thromboembolism.2

In conclusion, the data indicate that obesity is a risk factor for venous thromboembolism in men as well as women.