Thursday, July 25, 2013

Correlation and Causation

The Cancer Epidemiology journal reports on a correlation between a woman's height and her risk of post-menopausal cancer. They state:

Height was significantly positively associated with risk of all cancers (HR = 1.13; 95% CI, 1.11–1.16), as well as with cancers of the thyroid, rectum, kidney, endometrium, colorectum, colon, ovary, and breast, and with multiple myeloma and melanoma (range of HRs: 1.13 for breast cancer to 1.29 for multiple myeloma and thyroid cancer). These associations were generally insensitive to adjustment for confounders, and there was little evidence of effect modification.This study confirms the positive association of height with risk of all cancers and a substantial number of cancer sites. 

 The causal argument is that height means more active growth factors and more active growth factor means a higher chance for cancer.

Boy is that a stretch. Take melanoma, something for which I have a modicum of understanding (see my Draft book on Melanoma Genomics). Is height a causative agent? That in my opinion goes beyond being just a stretch. Frankly I cannot think of a single pathway, epigenetic, ECM, or other factor for which that works. 

The problem all too often is correlation is not causation. They both may have a similar cause, but that is left as an exercise for the reader. Although it gets great play from the Press (See NY Times):

Height can be influenced by a number of factors beyond genetics. The amount and type of foods consumed in childhood can influence height, and childhood nutrition may also play some role in cancer risk. A higher circulating level of a protein called insulin-like growth factor, which can be influenced by factors like exercise, stress, body mass index and nutrition, is also associated with both increased height and an increased cancer risk.

They found that for every 4-inch change in height, there was a 13 percent increase in risk for developing any type of cancer. The cancers most strongly associated with height were cancers of the kidney, rectum, thyroid and blood. Risk for those cancers increased by 23 to 29 percent for every 4-inch increase in height.

I would not worry too much about this issue. You see I am 6'3".