Hypertension detection and follow-up program study of serum retinol, retinol-binding protein, total carotenoids, and cancer risk: a summary.

In a recently reported study by us, no significant associations were found between retinol, retinol-binding protein (RBP), and total carotenoid levels in prediagnositic serum and the incidence of cancer at all sites combined. Inasmuch as other investigators, in addition to us, have not been able to confirm the two original reports of an inverse association between serum retinol and overall cancer incidence, the relationship, if it exists at all, is probably complex and limited to certain population subgroups. Such subgroups may be defined by extreme values of serum retinol, certain levels of other nutrients, or specific types of cancer. In the present study an inverse association was observed between serum retinol levels and cancer among subjects with low serum selenium levels and for subjects with gastrointestinal cancer. In addition, the risk of cancer was elevated for those individuals with the combination of low serum retinol and high RBP. However, since significant associations will arise by chance alone when many subgroups are examined, these findings are difficult to interpret. Additional studies will be needed to determine whether they are reproducible or are simply the results of chance.