Relationship Between Systemic Markers of Inflammation and Serum β-Carotene Levels

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Abstract
IN A LANDMARK article, Peto et al1 hypothesized that low intake of β-carotene was a modifiable risk factor for cancer. This hypothesis was strongly supported by the consistent finding of an inverse association between serum β-carotene level and risk of cardiovascular disease and certain types of cancer, especially lung cancer.2,3 However, in large-scale trials,4-10 supplementation of the diet with β-carotene either had no benefit or caused harm. There are several possible explanations for the discrepancy between results of observational studies and clinical trials,2 including the possibility of confounding by other nutrients or lifestyle factors that might be associated with β-carotene intake. An alternative explanation is that serum β-carotene levels reflect not only β-carotene intake but also other physiologic processes related to disease occurrence. In that case, low serum β-carotene concentration might be an epiphenomenon, and increased intake of β-carotene would not be expected to reduce the risk of disease. Although this is a well-known theoretical limitation of serum biomarkers, it is seldom considered in the interpretation of biomarker data.

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