Thursday, July 28, 2011

More on cancer & height

The information contained in the summary report on height and cancer incidence in Lancet Oncology which I have seen concentrates on the results of an analysis of the Million Women Study, a prospective study which recruited its subjects from among those who received AND accepted an invitation to the UK national breast cancer screening programme between 1996 & 2001.

The height analysis included some 1.3 million middle aged women (born between 1931 & 1951) who were followed for an average of over 9 years. During this time 97 376 cancers were diagnosed in these women, so, in crude terms, the overall cancer risk was about 1 in 13.

The summary does not unfortunately provide any information about the height distribution of the women but I have used information on average heights by age from the Health Survey England to make a rough estimate of a mean height of 5ft 3” with fewer than 1 in 20 women outside the range 4ft 10” to 5ft 8”, so to rely on this sample alone for extrapolation beyond these limits, & to men, is somewhat heroic. Unfortunately for me the summary simply refers, without details of the populations studied, to a meta-analysis which included ten other prospective studies, which also showed a height risk for cancer across Europe, North America, Australasia, and Asia.

Although the overall cancer risk in the Million Women increased with height, the results were significant for cancers in only ten of the 17 separate sites studied – in two of them there was no increase, & in 5 the increase was not statistically significant.

I should be very interested to see the strength of the evidence for men. Height makes a man happy, but is more problematic for a woman, so perhaps the cancer-inducing mechanism is after all a psychological one.

Curiously, in current smokers, smoking-related cancers were not as strongly related to height as were other cancers, so perhaps there is something in my long lung theory after all!

Finally, it is worth reminding ourselves of Galton’s view of the causes of variation in height:

… Stature is not a simple element, but a sum of the accumulated lengths or thicknesses of more than a hundred bodily parts, each as distinct from the rest as to have earned a name by which it can be specified. The list … includes about 50 separate bones, situated in the skull, the spine, the pelvis, the two legs & the two ankles & feet. The bones in both the lower limbs are counted, because it is the average of these two limbs that contributes to the general stature. The cartilages interposed between the bones, two at each joint, are rather more numerous than the bones themselves. The fleshy parts of the scalp of the head & of the soles of the feet conclude the list. Account should be also taken of the shape & set of many of the bones which conduce to a more or less arched instep, straight back, or high head …

The beautiful regularity in the statures of a population, whenever they are marshalled in order of their heights, is due to the number of variable elements of which stature is the sum …

It is hard to think of a single cause, or mechanism, which produces all these differences & could translate into a cause (or causes) for cancer.


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