That blood clot risk was lowest among the shortest women and men and appeared to increase with height, the research showed.
“Height is not something we can do anything about,” lead study author Dr. Bengt Zöller, associate professor at Lund University and Malmö University Hospital in Sweden, said in a news release.
“However, the height in the population has increased, and continues increasing, which could be contributing to the fact that the incidence of thrombosis has increased,” he said. “I think we should start to include height in risk assessment just as overweight, although formal studies are needed to determine exactly how height interacts with inherited blood disorders and other conditions.”
The new blood clot study involved data on more than 1.6 million Swedish men who enlisted in the military and were born between 1951 and 1992, and data on more than 1 million Swedish women who had a first pregnancy between 1982 and 2012. Pregnancy can increase the risk of blood clots, which is among the leading causes of maternal deathin the developed world.
How dangerous are blood clots?
Using the Swedish Multi-generation Register, the researchers identified siblings of different heights. They also used the national Swedish Hospital Register to track hospital inpatient and outpatient diagnoses of blood clots between 1969 and 2012.
The researchers found that the risk for blood clots decreased 69% for women shorter than about 5-foot-1, compared with women about 6 feet and taller. The risk dropped 65% for men shorter than about 5-foot-3, compared with men about 6-foot-2 and taller, the researchers found.
Among men, an association with height was found for risk of blood clots in the lungs, called pulmonary embolism, as well as in the legs and other locations. Among women, only the risk of blood clots in the legs was significantly associated with height.
Still, “these clots are deadly because they can break free from the vein and travel to the lung,” said Dr. Mary Cushman, professor of medicine and pathology and director of the Thrombosis and Hemostasis Program at the Larner College of Medicine at the University of Vermont, who was not involved the new study.
“If the clot is big enough, that can cause death, which is sometimes sudden,” she said.
The researchers also found that the strong association between blood clot risk and height remained among the siblings.
The strengths of the new study are its large sample sizes and its utilization of siblings, said Dr. Nesochi Okeke-Igbokwe, an attending physician of internal medicine at NYU Langone Health in New York, who was not involved in the new study.
“Overall, it is a solid study with good research methodology used,” Okeke-Igbokwe said.
“The bottom line regarding this recent study, whether you are a taller or shorter individual, you must be aware of all the additional lifestyle factors that may increase your risk for blood clots, such as smoking or a sedentary lifestyle,” she said. “We have no control over our height, but we certainly can all take the appropriate measures in making healthy lifestyle choices to reduce the risk of various conditions.”
One limitation of the study was that the researchers did not have information on the participants’ childhoods, home environments and diets. However, they used educational level as a measure of lifestyle factors.
All in all, “this study adds to growing evidence that body size in general is an important factor to consider in determining the risk of VTE. It also gives us information about why VTE occurs in the legs more often than elsewhere, like the arms,” said Cushman, who also serves as editor-in-chief of the journal Research and Practice in Thrombosis and Haemostasis.
“Basically, the blood has to travel up a vein against gravity, and when there is a longer distance to travel, there is more opportunity for the blood to clot abnormally,” she said. “This is not the case in the arms, for example, where arm movement allows blood to more easily flow out of the limb with the help of gravity.”
When it comes to the new study, the “robust” design could be replicated to determine whether height correlates with other health problems, said Ulhas Naik, professor of medicine and director of the Cardeza Center for Vascular Biology Research at the Sidney Kimmel Medical College at Thomas Jefferson University, who was not involved in the new study.
“Being tall, there are benefits in some ways in some diseases, (and) there is the opposite in some other diseases,” he said. “This kind of a study is a good starting point to now look at other diseases.”
A systematic review paper published in the journal Plos Medicine last year, in which 63 studies on the association of height with cancer risk were analyzed, provided evidence for a potential link between adult height and the risk of colorectal and lung cancers.
The paper also suggested that certain genetic factors and biological pathways affecting adult height may affect the risk of those cancers.
As with the Plos Medicine study, the researchers behind the 2015 study pointed to certain genetic factors and biological pathways affecting height as having an important role in the development of breast cancer.
Is short stature tied to gestational diabetes risk?
Height also has been linked to gestational diabetes, which occurs when high blood sugar starts or is first diagnosed during pregnancy.
Gestational diabetes affects mom, baby
A study of 135,861 pregnancies in women of various races in the US, of whom 5,567 were diagnosed with gestational diabetes, found that taller height was significantly associated with a lower risk of gestational diabetes.
Overall, women in the highest height quartile in that study had more than 60% lower risk of gestational diabetes compared with women in the lowest quartile, even after accounting for maternal age, weight, race, insurance and education, according to the findings.
Overall, a meta-analysis research paper on height and health risks, published in the International Journal of Epidemiology in 2012, found that “height was negatively associated with death from coronary disease, stroke subtypes, heart failure, stomach and oral cancers, chronic obstructive pulmonary disease, mental disorders, liver disease and external causes,” according to the abstract.
“In contrast, height was positively associated with death from ruptured aortic aneurysm, pulmonary embolism, melanoma and cancers of the pancreas, endocrine and nervous systems, ovary, breast, prostate, colorectum, blood and lung,” the abstract said. That study involved an analysis of 121 prospective studies including about 1 million people.
See the latest news and share your comments with CNN Health on Facebook and Twitter.