MAIN RESULTS:

1. BMI, waist circumference, hip circumference and waist-hip ratio all associate with venous thromboembolism.
2. Weight gain is linked to increased risk of venous thromboembolism, especially in those who are already obese.
3. Low-grade inflammation explains some of the association between obesity and venous thromboembolism.

THESIS DEFENCE:

Thesis: Obesity, body height and risk of venous thromboembolism
Candidate: Lars Daae Horvei
Time: January 18, 2018 at 11:15
Place: Medicine and Health Studies Building, UiT The Arctic University of Norway: Large Auditorium
Link to university website (in Norwegian)

SUMMARY:

(1) Horvei and coworkers used data on four different measures of obesity (BMI, waist circumference, hip circumference and waist-hip ratio) from more than 6000 participants in the fourth wave of the Tromsø Study. Almost 300 had venous thromboembolism within the next 16 years, whereas more than 900 suffered from a myocardial infarction. Increased values of at least one of the four obesity measures were linked to increased risk of both venous thromboembolism and myocardial infarction.

Regarding myocardial infarction, the associations decreased when the analyses were adjusted for traditional cardiovascular risk factors, but for venous thromboembolism the associations remained. The results imply that the link between obesity and venous thromboembolism is explained by other, unknown mechanisms.

(2) Obesity-related inflammation might be one of these explanatory factors. Plasma levels of C-reactive protein (CRP) reflect general inflammation, and CRP is formed when inflammatory markers are released from adipose tissue. The second article of Horvei’s PhD thesis shows a decreased association between obesity and venous thromboembolism when adjusting for CRP. This study includes almost 15 000 individuals who participated in the Tromsø Study between 1994 and 2008.

(3) I the third article, the researchers looked at the importance of weight change over time, using information from almost 18 000 men and women who have participated in at least two versions of the Tromsø Study. Those who gained more than 7,5 kilograms between two surveys had almost double the risk of venous thromboembolism compared to those  who gained less. For those who were already obese in the first survey and gained more weight before the next, the risk was increased by almost four times.

(4) Some genes increase the risk of venous thromboembolism, and the latest study by Horvei and colleagues suggests that the increased genetic risk is independent of a person’s height. Tall persons are at higher risk of venous thromboembolism, but the risk genes seem to have no impact on this association.

REFERENCES:

(1) Horvei, L. D., Brækkan, S. K., Mathiesen, E. B., Njølstad, I., Wilsgaard, T., & Hansen, J. B. (2014). Obesity measures and risk of venous thromboembolism and myocardial infarction. European journal of epidemiology, 29(11), 821-830.

(2) Horvei, L. D., Grimnes, G., Hindberg, K., Mathiesen, E. B., Njølstad, I., Wilsgaard, T., Brox, J., Brækkan, S. K. & Hansen, J. B. (2016). C‐reactive protein, obesity, and risk of arterial and venous thrombosis. Journal of Thrombosis and Haemostasis.

(2) Horvei, L. D., Brækkan, S. K., & Hansen, J. B. (2016). Weight change and risk of venous thromboembolism: The Tromsø Study. PloS one, 11(12), e0168878.

(3) Horvei, L. D., Brækkan, S. K., Smith, E. N., Solomon, T., Hindberg, K., Frazer, K. A., Rosendaal, F. R., & Hansen, J. B. (2017). Joint effects of prothrombotic genotypes and body height on the risk of venous thromboembolism: The Tromsø Study. Journal of Thrombosis and Haemostasis.