Taller people have a greater risk of cancer because they are bigger and so have more cells in their bodies in which dangerous mutations can occur, new research has suggested.
A number of studies have previously found a link between a lofty stature and a greater risk of developing some form of cancer, with research suggesting that for every 10cm of height within the typical range for humans, the risk increases by about 10%. A similar link has also been found in dogs, with bigger breeds having a greater risk of such diseases.
Scientists have put forward a number of different explanations for this, including that certain growth hormones could play a role in both height and cancer, or that environmental factors such as childhood nutrition or illness could be a factor.
“One of the major hypotheses was that something was happening early in life that was making your cells more susceptible to cancer and, sort of incidentally, causing you to be tall,” said Leonard Nunney, professor of biology at the University of California Riverside.
But now Nunney says he has crunched the numbers to show it might be down to a simpler matter of size: tall people simply have more cells for something to go wrong in.
Nunney said his work, published in the Proceedings of the Royal Society B, is based on the fundamental model of how cancer develops, whereby individuals accumulate mutations in their cells (other than sperm or eggs) over their life: if a particular set of mutations arise then a certain cancer will initiate. The theory suggests that having more cells, or more divisions per cell, would therefore increase cancer risk.
Nunney compared the overall risk of men and women developing cancer of any type with increasing height, as found from previous studies of large cohorts, with what might be expected from calculations based on the number of cells in a body.
The results reveal that his predictions are in tune with the real-life observations, giving a 13% increased risk for women for every additional 10cm in height compared with 12% from observations, and an 11% predicted increase in men for every 10cm taller compared with 9% seen in real life.
Overall, an increased risk with height was seen for 18 out of 23 cancers considered. Nunney says some cancers may have shown no link because the effect of height was masked by other drivers such as HPV infection for cervical cancer.
Nonetheless, Nunney says the findings suggest sheer number of cells is important. “Whether that comes from a better diet or the fact that your parents happen to be tall doesn’t matter … it is purely a number of cells, however that comes about,” he said, although he admits height differences only appear to partly explain why men are at greater risk of many cancers than women.
The research also threw up some surprises: for example, the skin cancer melanoma shows a much stronger link to height than expected – something Nunney suggests might be down to taller people having slightly higher levels of a growth hormone called IGF-1.
Nunney said a slight boost in the rate of cell division, as a result of higher levels of IGF-1, might have a stronger effect on these cells than it does in other tissues, possibly because melanoma might need a larger set of mutations to develop than other cancers.
Prof Dorothy Bennett, director of the Molecular and Clinical Sciences Research Institute at St George’s, University of London, welcomed the research, although she said Nunney’s calculations involved a number of assumptions, including that cancer risk increases in direct proportion to adult height.
But she said the argument was compelling: “The simplifications seem reasonable, and therefore the main study conclusion is probably going to be the best-supported one available at present: namely that for most cancer types, cell number can predict sufficiently well the numerical relations between height and cancer, with no need to suggest additional factors.”
That said, Bennett said there was no obvious reason melanoma should have a particularly strong link to height.
Georgina Hill, from Cancer Research UK, said individuals should not be concerned about their stature. “A number of studies over the years have shown that taller people seem to have a slightly higher risk of cancer,” she said. “But the increased risk is small and there’s plenty you can do to reduce the risk of developing cancer, such as not smoking and keeping a healthy weight.”