According to a study published in the journal Internal Medicine, being overweight in childhood and early adulthood are distinct risk factors for blood clots later in life. The study was based on the BMI histories of more than 37,000 male participants and information on any adult thrombi, if applicable. The researchers stated that blood clots and obesity have a known relationship. They added that their main goal was to shed light on the relationships between early-life BMI and future thrombi.

Thrombi typically start in a blood artery in the calf and develop in the legs. Some common symptoms include redness, discomfort, and swelling. Clots are rarely deadly when treated quickly. The subsequent "pulmonary embolism" could be fatal if one escapes and travels to the lungs in the bloodstream and sticks to the vessel wall there.

In the current study, 37,672 Swedish men born between 1945 and 1961 were included, and data such as measurements of height, weight, and BMI were collected from the records of the men, first from school health care services (at the age of 8 years), then from medical exams taken prior to enlisting in the armed forces (at the age of 20), as well as registering information on any blood clots up to an average age of 62.

The findings of the study showed that BMI at ages 8 and 20 were associated with an increased risk of venous blood clots when considered separately. The results showed that the clot can develop in the lung or the leg. Additionally, two groups were discovered to have a noticeably higher risk of venous thromboembolism with maturity. The first group consisted of people who had been overweight both as children and as young adults, whereas the second group included people whose weight as children was normal and who didn′t start being overweight until they were in their early 20s.

Furthermore, the researchers observed that being overweight as a child or young adult increased the chance of arterial thrombi, or blood clots, which were brought on by fatty deposits and inflammation narrowing blood channels. 

(Source: https://health.economictimes.indiatimes.com/news/diagnostics/childhood-obesity-is-a-risk-factor-for-blood-clots-as-adult-study/98383976 )