Women's chances of developing cancer after menopause increase with their height, according to a new study.
Among nearly 145,000 women between the ages of 50 and 79, researchers found that height was more strongly associated with cancer than such established risk factors as obesity.
The association held true for everything from thyroid cancer to melanoma, researchers reported in the latest issue of Cancer Epidemiology, Biomarkers and Prevention, a journal of the American Association for Cancer Research.
'The increase in risk is modest and is balanced by a lower risk of cardiovascular disease in taller people, so there is no reason for those of us who are tall to panic.' —Walter Willett, Harvard School of Public Health
It's not height itself that's the risk factor, though. The authors of the new study say height "should be thought of as a marker for one or more exposures that influence cancer risk, rather than a risk factor itself."
"There's an intriguing indication that things going on in early life appear to feed into a process that may increase the risk for various cancers," said Geoffrey Kabat, lead author of the study and a senior epidemiologist at Albert Einstein College of Medicine of Yeshiva University in New York.
Those things might include diet as well as hormones in the body that contribute to normal growth, although researchers aren't sure yet.
Cancer involves the uncontrolled division of abnormal cells in processes having to do with growth, so it follows that hormones or other growth factors that influence height may also influence cancer risk, Kabat said in a telephone interview with Reuters.
Walter Willett, chair of the department of nutrition at the Harvard School of Public Health, said the study should not raise alarm for the tall, though it does provide additional evidence that greater height is associated with cancer.
"The increase in risk is modest and is balanced by a lower risk of cardiovascular disease in taller people, so there is no reason for those of us who are tall to panic," Willett, who was not involved in the study, said in an email. "Most importantly, research to understand the reason for the extra risk in taller people may lead us to new ways to prevent or treat cancer."
Extra 10 cm increases cancer risk
The postmenopausal women in the study were participants in the Women's Health Initiative, a 15-year research program established in 1991 by the National Institutes of Health and other agencies to address the most common causes of death, disability and poor quality of life in postmenopausal women.
Altogether the researchers tracked 144,701 women for an average of 12 years, during which 20,928 of them developed new cancers.
Even after adjusting for such factors as body mass index — a ratio of weight in relation to height —the women's risk of developing any cancer rose by 13 per cent for every 10-centimetre increase in height, the researchers say.
With every extra 10 centimetres, researchers found, women's risk for cancers of the kidney, rectum, thyroid or blood rose by 23 to 29 per cent, and their risk of melanoma and cancers of the breast, ovary, endometrium or colon rose by 13 to 17 per cent.
According to the American Cancer Society, the average woman's lifetime risk of cancer is 38.2 per cent.
Other large studies have identified an association between height and certain cancers, but most of those studies didn't rule out the influence of other factors.
Kabat and his colleagues say they took more than a dozen potential risk factors into account —including age, use of oral contraceptives, smoking history, alcohol intake, age at their first menstrual period, and education — and they still found that women's height was linked to their cancer risk.
"At this point it seems to be a plausible mechanism whereby early nutrition could affect growth and cancer," Kabat said.
For example, tallness is tied to greater consumption of milk proteins by rapidly growing pre-pubescent girls, and in some studies milk intake has been linked with higher levels of a certain protein that may play a role in some of the abnormal cellular processes seen in cancers.
"It is also possible that the larger organ size and skin surface area associated with greater height may put more cells at risk of being transformed to malignancies," Kabat said.
Two previous studies reported that the correlation between height and any type of cancer was stronger among women who had never smoked, but Kabat and his colleagues found the correlation did not differ by smoking level.