Bad news, tall people: Your extra inches are increasing your likelihood of developing cancer. And the taller you are, the worse it is. Here's what that means for you, your sunscreen use, and the Dutch.
A study in the UK followed almost 1.3 million women for about 9 years. The women were middle-aged and had not had cancer before. Over the following years, researchers kept track of which women developed cancers. They also sorted the women into groups by height. What emerged was a tidy correlation: Compared to a very short woman (under 5 foot 1), every extra 10 centimeters in height increases your overall cancer risk by about 16%. At 5 foot 5, your cancer risk is about 20% greater than the short woman. And if you're 5 foot 9 or taller, you have a 37% greater chance of developing cancer than your 5-foot-tall friend.
Your height isn't totally independent from other variables in your life. Height is related to nutrition and health in childhood, and correlates with socioeconomic status. In addition to being wealthier, tall women in the study were more active, had fewer children, and were less likely to smoke or be obese (though they did drink more). However, when the researchers controlled for all of these variables--in addition to age, BMI, geography, and use of hormonal birth control--the height effect remained.
The researchers also analyzed 10 other, similar studies, applying to men and women on other continents. Overall, these studies came to almost the same conclusion: cancer risk went up by 14% for each 10 centimeters in height.
In the British study, some specific types of cancer had especially strong increases associated with height. Colon cancer, kidney cancer and leukemia risks increased by about 25% with every 10 centimeters in height, while the risk of malignant melanoma (skin cancer) increased by 32%.
Of course, tall people have more skin cells to start with. (And they're closer to the sun!) In fact, tall people have more cells overall. Is the height effect simply a cell-number effect? Does having more cells just create more opportunities for a cell to go rogue? It seems like the simplest explanation.
But the authors also wonder if higher circulating levels of growth hormones in childhood and adulthood, which are known to be linked to cancer, could be at fault. Another recent study found that Ecuadorians with a rare type of dwarfism, whose bodies don't respond to growth hormones, almost never get cancer. It's an intriguing hint that something more than mathematics is at work.
A 15% increase in risk can be more or less of a cause for alarm, depending on your starting point. If a certain type of cancer affects 1 in 100 people, a 15% increase means it now affects 1.15 out of 100 people: essentially, still just the one person. For something like breast cancer, which affects closer to 1 in 8 women, that 15% is more meaningful. Given all the other risk factors in an individual person's life, though--known and unknown--a 15% increase could be easily overwhelmed by other variables. Smoking, for example, increases your risk of lung cancer by something like 2,300%. Having a million-person study gave the authors the statistical power to find much smaller effects.
Even if the increase in risk is small, it might be noteworthy globally, given that the populations of many countries are growing taller as they become wealthier. The authors say that during the 20th century, heights throughout Europe increased by about 1 centimeter per decade. This factor alone might have increased cancer incidence by 10 or 15%.
Maybe we should stop feeling sore about the Dutch becoming the tallest people in the world while our own populace lags behind various Scandinavian nations. At least we don't have the top cancer rates! (While we're at it, we can stop blaming our cell phones, too.)
Green, J., Cairns, B., Casabonne, D., Wright, F., Reeves, G., & Beral, V. (2011). Height and cancer incidence in the Million Women Study: prospective cohort, and meta-analysis of prospective studies of height and total cancer risk The Lancet Oncology DOI: 10.1016/S1470-2045(11)70154-1
Book review: Leonard Mlodinow's "The Upright Thinkers:The Human Journey from Living in Trees to Understanding the Cosmos"
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