Serum retinol and subsequent risk of cancer

In a prospective study of about 22,000 men attending a well person screening centre, serum samples were collected and stored. The concentration of retinol was measured in the stored serum samples from 227 men subsequently notified as having cancer and from 454 unaffected controls, matched for age, smoking history and duration of storage of the serum samples. The mean serum retinol concentration of the cancer subjects who developed cancer before the elapse of one year since the time blood was collected was significantly lower than the mean concentration of their matched controls (641 and 722 micrograms l-1 respectively, P less than 0.001). For subjects whose cancer developed one to two years after blood had been collected, the difference was less (650 and 701 micrograms l-1 respectively, P less than 0.01). For subjects whose cancer developed three or more years after blood was collected, the mean retinol level was higher than in their controls, although not statistically significantly so (694 and 663 micrograms l-1 respectively). These findings suggest that the inverse association between serum retinol and risk of cancer that was previously observed was due to low serum retinol being a metabolic consequence of cancer rather than a precursor of cancer.