Here’s a fact that has fascinated scientists for decades: Your risk of cancer is associated with how tall you are.
No one is quite sure why. Is it influenced by our genes, our environment or both? Even after hundreds of studies the jury is still out. But what is now accepted is that the link is real.
What’s more, the risk has been growing for the last 150 years, because on average people have been getting taller. Here’s the full story. . .
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As height increases, so does cancer risk
Colorectal Cancer: In a meta-analysis of 16 studies, participants in the top height categories had between 20% and 60% increased risk compared to those in the bottom height categories.
For instance, in a study of over a million Norwegians, 6,397 men developed colon cancer and 4,393 developed rectal cancer. The figures for women were 7,620 and 3,482.
They were divided into five groups according to height, ranging from the shortest one-fifth to the tallest one-fifth. That put about 200,000 men in each group.
Men in the top height group had a 37% increased risk of colon cancer and a 17% increased risk of rectal cancer compared to those in the bottom height group. For women the figures were 35% and 18%.
In another group of 13 studies that combined the results of 5,287 cases of colorectal cancer, there was a consistent height/cancer association with the tallest men and women having a 31% increased risk compared to the shortest.
In April, 2016, Guillaume Onyeaghala of the University of Minnesota reported on a new study at the annual meeting of the American Association for Cancer Research. It showed that the group in the top quarter of leg length were 42% more likely to get colon cancer than those in the bottom quarter.
And those with the very longest legs (35.4 inches) had a 91% greater risk than those with the shortest legs (31.1 inches).
Prostate Cancer: Most of the 22 studies analyzed reported a 20% to 40% increased risk in those in the top height categories compared to the bottom.
In a study of 22,071 US male physicians, there were 1,047 cases of prostate cancer. The doctors who were more than 6 feet tall had a 26% greater risk compared to those under 5 feet 7 inches.
In another study of 47,781 US male health professionals, 1,369 were diagnosed with prostate cancer. Those 6 feet 2 inches or taller were found to be at a 37% greater risk of this common cancer than those 5 feet 8 inches tall, or less.
The researchers also reported “that tallness had a strong direct association with risk of metastatic disease,” with an increased risk of 68%.
Breast Cancer: In a group of 24 studies there was an increased risk ranging from 10% to 60% in the tallest height categories compared to the shortest.
In a study of 62,573 women aged 55 to 69 from the Netherlands, 626 had breast cancer after a four year follow up. The researchers found “a significantly positive association between adult height and breast cancer.” The risk for women over 5 feet 9 inches was double that of women who were 5 feet or less.
Endometrial/uterine cancer: Above average versus below average heights of 570,000 Norwegian women were compared. The 2,208 women with uterine cancer who were taller than average had a 20% greater risk.
The conclusion of another study that compared women with endometrial cancer with those free of the disease (controls) concluded that “women with endometrial cancer were significantly taller than control women.”
Other cancers: Increasing height has been found to increase the risk of a number of other cancers.
In 2010 the British Journal of Cancer published a study which showed that for every additional two inches of height the risk of developing testicular cancer increased by 13%. The relationship has also been found in cancers of the blood, lymphatic system, thyroid, ovary and some others.
Are the studies reliable?
One of the problems with conducting population studies is that it isn’t always clear what is being measured. For instance, taller people will tend to weigh more, so it may be weight that correlates with cancer and not height.
Higher socioeconomic status is also associated with greater stature. To put it bluntly, rich and powerful people also tend to be taller, on average. Perhaps such people are more health conscious and are more likely to request screening, which detects cancer at an early stage.
The number of potential biases in such research (confounding factors) can seriously skew the results.
The very best studies use very large population sizes and take as many confounding factors into account as they can. However, most studies have suffered to some degree from such biases.
The biggest studies confirm the link
The biggest study of its kind involved over five million Swedish people over a 50-year period.
The researchers discovered that for every four-inch increase in height, the risk of developing any form of cancer increased by 11% in men and 18% in women. The risk of malignant melanoma increased by 32% in men and 27% in women. The analysis took education and income into account.
The Million Women Study of 2011 is the most reliable of all the studies because it included 1,300,000 women and took a huge number of factors into account.
For every four inches above 5 feet, the cancer risk increased by 16% for 10 different cancers. Women in the study who were more than 5 feet 9 inches tall were 37% more likely to develop cancer than those under 5 feet.
The researchers took into account year of birth, socioeconomic factors, alcohol intake, body mass index, physical activity, age at puberty, number of pregnancies, age at first birth, menopausal status, use of hormone replacement therapy and smoking.
Finally, a study of 788,789 Koreans that took into account age, body mass index, female reproductive factors, and behavioral and socioeconomic factors found that every two inch increment in height was associated with a 5% higher cancer risk for men and 7% for women at all cancer sites.
How height increases cancer risk
The evidence for the height/cancer link is convincing, but the reason for the connection is not known.
Dr. Jane Green from Oxford University, who was lead researcher in the Million Women Study, said, “Obviously height itself cannot affect cancer, but it may be a marker for something else.”
What is that something else? Nobody knows for sure, but various ideas have been put forward.
- Genetics – 80% of height variation in Western societies is thought to be accounted for by 180 separate genetic markers that could also increase cancer risk.
- Organ mass and skin surface area – the organs and skin surface area of taller people are greater in size. More body cells may make for a greater likelihood of mutation.
- Infections – some pathogens are known to cause cancer. A lower infection load in early childhood could increase risk of cancer if the infections are experienced later in childhood or as adults. Fewer infections in childhood may also lead to underdevelopment of the immune system.
- Birth weight – risks of prostate and breast cancer have been linked to higher birth weight, which in turn is associated with greater height.
- Nutrition – higher calorie intake in childhood and adolescence or greater intake of milk proteins
- Growth hormones – insulin-like growth factor (IGF-1) plays a fundamental role in body growth. Levels of IGF-1 increase in puberty and drive skeletal growth. An excess of this hormone and/or a decrease in its main binding protein, IGF-3, has been strongly linked to many different cancers. Cow’s milk contains high levels of IGF-1.
In a recent paper published in the journal Lancet, four medical professors wrote that for every 2½ inches in height, cancer mortality increases by 4%. They believe this is caused by too much high calorie food, in particular milk, dairy and other animal protein during fetal and child development and its influence on IGF-1.
In their view, “Limiting over-nutrition during pregnancy, early childhood and puberty would avoid not only obesity but also accelerated growth in children – and thus might reduce risk of cancer in adulthood.”
If you are especially tall, there is some good news. You have a lower risk for cardiovascular disease and type 2 diabetes.