Friday October 2 2015
Tall people shouldn't lose any sleep over study into height and cancer
"Higher risk of cancer if you are tall," says the Daily Mirror. Most media outlets provided a similar spin on the seemingly big news that the risk of developing cancer increases with every 10cm of height.
Tall people shouldn't lose any sleep over this news: let's face it, there's nothing you can do about your height (although there are plenty of things you can do to reduce your risk of cancer). What's more, the research these stories are based on does not provide proof being tall means you will get cancer.
Currently, only preliminary results have been presented in the form of a conference abstract, and the research hasn't had the kind of independent rigorous scrutiny you'd hope for in published science.
That's not to say this was bad research: the study was large, involving 5.5 million adults, which is usually a good thing. However, it did not take into account many known risk factors for cancer, such as smoking.
Neither the study nor any of the papers covering the story suggested adult height directly causes cancer. Theories presented in the media about why being taller would increase cancer risk are simply speculation – no matter how well informed they are.
Where did the story come from?
The study was carried out by researchers from Karolinska Institute in Stockholm and was funded by HKH Kronprinsessan Lovisas förening för Barnasjukvård and Stiftelsen Samariten.
It was summarised briefly ahead of the European Society for Paediatric Endocrinology conference in a very short article called a conference abstract. This means there is little detail on the methods and results presented, and its strengths and weaknesses can't be appraised in any depth.
It has not yet been published in a peer reviewed journal, so the research hasn't been scrutinised by experts for scientific accuracy or rigour.
Generally, the media reported the story accurately. It was made clear that no-one was saying being tall causes cancer directly. However, because the actual science was not presented in great detail, most padded out their copy with speculation about what could cause the link between being tall and cancer. Fortunately, the media outlets that did this tended to use independent and informed commentators.
What kind of research was this?
This was a cohort study of a very large group of mostly Swedish adults over several decades. The researchers were looking for a link between height and risk of cancer.
Previous studies have linked being taller with a higher risk of developing cancer overall – breast cancer and skin cancer in particular – and this was also the focus of the new study.
According to media reports, the research team don't believe increased height directly causes cancer. Instead, height is thought to be a marker of other factors that raise the risk of cancer.
One theory presented in the media is that taller people have more cells in their body growing and dividing, with more potential to undergo cancerous change. The higher food intake needed to maintain a larger body size may also play a part.
For this particular study, the researchers were less interested in explaining exactly how height might be linked to cancer risk – they first wanted to establish whether height was linked to cancer.
Apparently, the topic hadn't been studied on a large scale before. Using a large group of people, as they did, increases the chances of finding a true link if one exists, and also increases the accuracy of any calculations of the risk.
What did the research involve?
The researchers tracked 5.5 million Swedish adults aged over 20 over several decades, although the average time was not reported in the brief summary available.
Sweden has very complete information on its residents. This meant it was relatively simple for the researchers to get height measurements from a combination of military conscription records and passports. These heights ranged from 3 feet 3 inches (100cm) to 7 feet 5 inches (225cm).
The researchers were also able to easily link the height data to medical records showing when a person was diagnosed with cancer and the cancer type.
The team then calculated the risk of people getting cancer for every 10cm increase in height. They worked this out for men and women separately, working out the risk for cancer overall and separately for breast cancer and skin cancer.
Adjustments were made for education level and income, which are known to influence both height and cancer risk. There was no adjustment for smoking, alcohol intake, sun exposure or other factors known to affect cancer risk.
What were the basic results?
The results presented showed that:
- Both taller men and taller women had a higher risk of developing cancer overall. For every extra 10cm of height as an adult, the risk of cancer rose by 11% in men and 18% in women.
- For breast cancer, a 10cm increase in height raised the risk of breast cancer in women by 20%. As breast cancer is much rarer in men, their risk was not calculated.
- A 10cm increase in height raised the risk of skin cancer by 32% in men and 27% in women.
How did the researchers interpret the results?
Dr Emelie Benyi, who led the study, said the results could help identify risk factors that could lead to the development of treatments.
She added: "As the cause of cancer is multi-factorial, it is difficult to predict what impact our results have on cancer risk at the individual level."
This large, long-term cohort study was able to give precise estimates of the risk increase of cancer for taller adults.
Currently, this information has only been presented as a conference abstract and accompanying press release. It is not possible to fully assess the study's methods, strengths and limitations from this, but some potential limitations are apparent.
While the study clearly showed a link between height and cancer, it did not take into account a range of confounding factors known to affect cancer risk – things like smoking, alcohol intake and sun exposure.
The problem is cancer risk may be influenced by these factors – and potentially others – and may explain some or all of the risk increases linked to height here. This study really doesn't provide much in the way of an explanation of how height might be linked to cancer, although media reports mentioned a number of theories.
These theories were largely speculative. The study did not look at whether taller people were more likely to die of cancer, but this is something they plan to do in the future.
Tall people shouldn't be worried by this study. There is not much you can do as an adult to change your height. But the good news is there are many simple things you can do that may help reduce your risk of cancer – for example, eating a balanced, healthy diet, taking regular exercise, not smoking, and drinking alcohol in moderation.
Read more about how a healthy lifestyle can help reduce your chances of developing cancer.