Thursday July 21 2011
“Taller people are more likely to develop some of the commonest and deadliest cancers, the largest study of links between height and the disease has concluded,” reported The Guardian.
This study looked at the relationship between height and the incidence of 17 specific cancers in more than 1 million middle-aged women in the UK. Overall, the relative risk of getting cancer increases by 16% for every 10cm increase in height. The tallest women (over 175 cm) had a 37% increased risk of cancer, compared to the smallest group (less than 155 cm).
It is important to note that in terms of a woman’s actual risk of developing cancer, these increases are small. For example, for every thousand women in the tallest group [average height 173.8 cm] there will be 10 diagnoses of cancer in any given year, while for every thousand women in the shortest group [average height about 153cm] there will be 8 diagnoses of cancer in any given year. This equates to an additional 2 diagnoses per 1000 women per year in the tallest group versus the shorter group.
This large, well-conducted study took into account other risk factors for cancer, such as socio-economic status and smoking, which might otherwise be responsible for an apparent relationship between height and cancer risk. Its results are likely to be reliable. It also seems to confirm previous research which has found an association between height and cancer incidence.
Tall people should not be alarmed by the findings. While it seems likely that height plays a part in cancer risk, there are other well-established and possibly more important risk factors for cancer, including family history and lifestyle. Most importantly, height cannot be changed. But adopting a healthy diet, taking regular exercise, limiting alcohol intake and abstaining from smoking are active measures that can be taken to reduce cancer risk.
Where did the story come from?
The study was carried out by researchers from the University of Oxford and the Institut Català d'Oncologia in Barcelona. It was funded by Cancer Research UK and the UK Medical Research Council. The study was published in the peer-reviewed medical journal The Lancet.
The study was widely reported in the papers, which all used the relative increase in risk (a 16% risk increase) rather than looking at the difference in the percentage of women getting cancer in each height group. This was actually quite small, equating to about an increase in risk of 0.2% per person per year in the tallest group versus the shorter group. Some of the headlines on the cancer risk for tall people were a little alarmist. The Daily Mail’s assertion that “taller women are a third more likely to be diagnosed with cancer” is perhaps misleading. It refers to the increased risk for women of 175cm or above in height – the tallest group – when compared to the “reference” group of women measuring 155 cms or less. Looking at the differences in risk, women in this last group had a 6.8% risk of cancer compared to an 8.9% risk for women measuring 175cms or more. For every thousand women in the tallest group [average height 173.8 cm] there will be 10 diagnoses of cancer in any given year, while for every thousand women in the shortest group [average height about 153cm] there will be 8 diagnoses of cancer in any given year. This equates to an additional 2 diagnoses per 1000 women per year in the tallest group versus the shorter group.
What kind of research was this?
This prospective cohort study investigated the possible relationship between the incidence of 17 specific cancers and height in middle-aged women. The researchers also carried out a meta-analysis of published results from previous studies on the relationship between height and cancer occurrence or deaths from cancer, in both men and women.
The researchers say that while some studies have found an association between height and risk of cancer, it is unclear whether these risks vary across different cancers. It is also unclear how far other factors such as smoking and socio-economic status influence the risk. They point out that the range of height within a given population is usually narrow, which means that large numbers of people are needed for any study to evaluate risk.
What did the research involve?
The researchers used information from the Million Women Study, a UK cohort study of 1.3 million women in the UK who were invited to take part between 1996 and 2001. The women completed a questionnaire that included, among other things, information on height, weight, and on social, demographic and lifestyle factors relevant to cancer. A random sample of women was used to validate the correlation between measured and reported height.
The women, who had not had a previous cancer diagnosis, were then followed-up for an average of 9.4 years, to find out who and how many of them developed cancer.
For this study, the researchers looked at the incidence of 17 specific cancers. These were mouth and throat, oesophagus (food pipe), stomach, colon, rectum, pancreas, lung, malignant melanoma, breast, endometrium (lining of womb), ovary, kidney, bladder, central nervous system, non-Hodgkin’s lymphoma, multiple myeloma and leukaemia.
For the analyses, women were divided into six categories of reported height: less than 155cm, 155-159 cm, 160-164.9 cm,165-169.9cm, 170-174.9cm and 175cm and taller.
Women were excluded from the analysis if they had had any cancer (other than non-melanoma skin cancer) that had been diagnosed before recruitment. Also excluded were those who did not have valid information on height on recruitment.
The researchers used validated statistical methods to analyse the relationship between height and cancer incidence, calculating the relative risk increase per 10cm increase in height.
The findings were adjusted to take account of other risk factors for cancer, including age, socio-economic group, BMI and exercise, alcohol and smoking habits.
What were the basic results?
The researchers followed-up a total of 1,297,124 women for an average of 9.4 years per woman (a total of 11.7 million person-years). During this time, there were 97,376 cases of cancer.
For every 10 cm increase in height, the relative risk of getting any type of cancer rose by 16% (95% CI 1.14—1.17).
The relative risk increased for 15 of the 17 cancers that were assessed, and was statistically significant for 10 of these. These are listed below, with the figures indicating the increase in relative risk per 10cm in height for each cancer (95% confidence intervals are in brackets – the narrower this range the more precise the estimate):
- Colon cancer 25%, (19% —30%),
- Rectal cancer 14% (7% — 22%),
- Malignant melanoma 32% (24% — 40%),
- Breast 17% (15% — 19%),
- Endometrium 19% (13% — 24%),
- Ovary 17% (11% — 23%)
- Kidney 29% (19% — 41%),
- Central nervous system cancers 20% (12% — 29%),
- Non-Hodgkin’s lymphoma 21% (14% — 29%)
- Leukaemia 26% (15% — 38%).
They also found that the increase in overall risk of cancer per 10 cm increase in height did not vary significantly by socio-economic status or by a variety of other personal characteristics except for smoking: smoking reduced any effect of height on cancer risk. Also, perhaps unsurprisingly, smoking reduced any effect of height on risk of smoking-related cancers (RR per 10 cm increase in height 1.05, 95% CI 1.01—1.09 among current smokers, and 1.17, 1.13—1.22 among current non-smokers).
In a meta-analysis (i.e. a statistical aggregation) of this study and 10 other prospective studies, similar height-associated risks for total cancer were seen. They showed little variation across Europe, North America, Australasia and Asia. Although men in these studies also had a height related risk of cancer, overall, women’s height related risk was slightly higher than men’s.
How did the researchers interpret the results?
The researchers say that for most cancer sites, the risk of cancer increases with height and that this relationship is similar in different populations. They suggest that a basic common mechanism, possibly acting in early life, might be involved. Possible factors related to both height and cancer include childhood nutrition, infection and hormone levels (especially of certain growth factors). Another possible factor is the simple fact that taller people have more cells (including stem cells) and thus a greater opportunity for cell mutations to lead to cancer.
The relation between height and cancer risk might explain the changing incidence of cancer over time, say the authors. Therefore the increase in adult height during the past century could have resulted in an increase in cancers some 10-15% above that expected if height had remained constant.
This large study is of interest because it suggests that there may be certain factors that influence both height and cancer risk. It could therefore lead to further research into what these factors might be – and whether they can be modified to reduce the risk of cancer. Alternatively, as the researchers suggest, it could simply be that taller people have more cells and therefore a greater chance of cell mutations.
As cancer experts have pointed out, tall people should not be alarmed by the findings. Despite the large increases in relative risk, the absolute differences in cancer risk between women of different height was quite small and are likely to play a far smaller part than family history and genes, and most importantly, lifestyle factors such as smoking, which can be modified.