“Walking tall can increase a man's chances of developing testicular cancer,” reported The Independent. It said a study has found that for “every extra two inches in height, the risk of being diagnosed is raised by around 13%”.
This was a large well-designed review of past research of body size and the risk of testicular cancer. The researchers combined the results of 13 previous studies looking at the relationship between height and testicular cancer risk. Combining and re-analysing these data suggested that for every 5cm increase in height there was a 13% increase in risk.
The newspapers covered this study responsibly, all stating prominently that any potential link between height and testicular cancer risk is not fully understood and is not necessarily a causal one. Testicular cancer is rare and responds well to treatment. Even with an increased risk, tall men still have a low likelihood of developing the disease. Nonetheless, men of all heights should be aware of the symptoms and check with their doctor if they notice any changes to the size of their testicles. Visit the Health A-Z pages - testicular cancer to find out more.
Where did the story come from?
The study was carried out by researchers from Yale University and the National Cancer Institute in the US. It was published in the peer-reviewed British Journal of Cancer. No sources of funding are given.
The study was well-reported by BBC News, The Independent and the Daily Mail. They all explain that any potential link between height and testicular cancer risk is not fully understood and that individuals actually have a low risk of developing the disease. The BBC helpfully quotes experts as saying that the absolute risk for men in the UK is low - only one in every 210 men will develop the disease. The newspapers also quote the researchers, who say that family history is a more important risk factor. The Independent’s headline might be considered more alarming than is justified, considering the balance of the rest of the report.
What kind of research was this?
Previous research has suggested that height and weight can affect a man’s risk of developing testicular cancer. Here, the researchers carried out a systematic review of these studies. They searched four databases of medical literature to try to find all the studies that had been published on body size and the risk of testicular cancer. They then performed a meta-analysis of the studies, combining their results to give more power to the question of whether body size affects testicular cancer risk.
Adult height is influenced by a number of factors, including genetics, childhood health and nutrition. These factors also influence the risk of a number of other diseases.
Testicular cancer is rare, with around 2,000 new cases diagnosed in the UK each year. Most of the studies included in this research were case-control studies, which had specifically compared the height and weight of men with the disease to those without it. A meta-analysis is a valid way of exploring a potential relationship between a risk factor and a disease. One weakness is that in meta-analyses of case-control and cohort studies, the original studies may have been carried out in very different ways, affecting the accuracy of the combined result.
What did the research involve?
The researchers searched four large databases of medical literature for all studies that compared body size and the risk of testicular cancer. The search identified 14 studies that were suitable for inclusion in the analysis.
The results of these studies were combined for the meta analysis. The studies differed in several ways. For instance, weight was defined differently by different studies. Some recorded weight at a specific age (20 to 21), while others selected weight at cancer diagnosis or at some specified point prior to diagnosis. Height was defined as height at age 18 or older. The studies that were included in the final analysis all focused on testicular germ cell tumours, which are the most common type of testicular cancer.
The analysis was concerned with whether there was a relationship between testicular cancer risk and adult height, body mass index (BMI) or weight. The analysis of height involved 13 of the 14 studies, including 5,764 cases. The analysis of weight used 12 of the studies, including 5,505 cases. The analysis of BMI included 13 studies and 13,993 cases. Studies were excluded from a particular analysis if they did not report the relevant data for that risk factor. None of the analyses adjusted for other potentially influential lifestyle factors or family history.
What were the basic results?
The analysis of height and testicular cancer risk showed that the risk of cancer increased by 13% with every 5cm increase in height (OR=1.13, 95% confidence interval [CI] 1.07 to 1.19). The analysis of BMI showed that men who were overweight were less likely to develop testicular cancer compared with those of normal weight (OR 0.92, 95% CI 0.86 to 0.98). However, men who were obese were as likely to develop the disease as people of normal weight (OR 0.92, 95% CI 0.75 to 1.15). There was no association between weight and testicular cancer risk.
How did the researchers interpret the results?
The authors state that their research “provides support for a positive association between height and [testicular germ cell tumours (TGCT)], but little support for an association between weight and TGCT. Further investigation of the inverse relationship between BMI and TGCT may be warranted, for which the present findings lend only limited support.”
This study suggests that taller men may have a greater risk of developing testicular cancer. But it is not clear why this should be the case, or if height and cancer risk are both associated with some other factor (such as diet), which has a role to play in the risk of the disease.
A meta-analysis is a good way of gathering larger numbers of cases together than might be possible in a single study. There are, however, some potential limitations to this approach:
- The analysis only included studies that had been published. Problematically, some studies that do not find an association between a risk factor and a disease are not published. This creates a potential source of bias known as ‘publication bias’, which revolves around the idea that had these studies been included, a different result may have been achieved.
- Another limitation is that the individual case-control studies and cohort studies that are combined together in meta-analyses often have very different study methods, or the original analyses took into account different risk factors. These differences can affect the results.
- A well-conducted systematic review and meta-analysis can still give an inaccurate result if the studies on which it is based are poorly conducted.
- In this particular study, the researchers were not able to adjust their analysis to take into account other factors that might influence the association between body size and testicular cancer, such as lifestyle, socioeconomic factors or family history.
Overall, this is a well-designed study that suggests a useful avenue for further research. The results cannot be used to deduce whether this is a direct relationship or if some other factor is responsible for this link. Research on other factors associated with height, such as hormone levels or diet, may shed more light on this relationship.
Although testicular cancer is rare, all men should be aware of the signs and symptoms, regardless of their height. Visit the Health A-Z bundle to find out more.