Relationship between systemic markers of inflammation and serum beta-carotene levels.
BACKGROUND
Low serum levels of beta-carotene have been associated with increased risk of cancer and cardiovascular disease. However, in clinical trials, supplementation of the diet with beta-carotene either had no benefit or caused harm. This pattern of findings raises the possibility that confounding by other factors might explain the association between serum beta-carotene level and disease risk.


METHODS
We used data from 14 470 current smokers, ex-smokers, and never smokers aged 18 years or older who participated in the Third National Health and Nutrition Examination Survey to assess the relationship between serum beta-carotene and markers of inflammation (C-reactive protein and white blood cell count).


RESULTS
After adjustment for beta-carotene intake and other factors, geometric mean levels of serum beta-carotene for individuals with undetectable (< 0.22 mg/dL), mildly elevated (0.22-0.99 mg/dL), and clinically elevated (> or =1.0 mg/dL) C-reactive protein levels were 18.0, 16.1, and 13.6 microg/dL, respectively, in never smokers; 18.1, 15.7, and 13.9 microg/dL in ex-smokers; and 11.3, 10.2, and 9.4 microg/dL in current smokers (P< .001 for all). In corresponding analyses, white blood cell count was also inversely related to serum beta-carotene concentration (P< .05 for all).


CONCLUSIONS
The strong and inverse association of serum beta-carotene level with C-reactive protein level and white blood cell count suggests that the relationship between serum beta-carotene concentration and disease risk might be confounded by inflammation. More broadly, for beta-carotene and likely other nutrients, it seems unwise to interpret biomarker data as prima facie evidence of dietary intake without a more complete understanding of the physiologic processes that affect nutrient levels.
Erlinger
T P
TP
Welch Center for Prevention, Epidemiology, and Clinical Research, Johns Hopkins Medical Institutions, 2024 E Monument St, Suite 2-600, Baltimore, MD 21205, USA. terlinge@jhmi.edu
Guallar
E
E
Miller
E R
ER
Stolzenberg-Solomon
R
R
Appel
L J
LJ
D000328:Adult; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000378:metabolism*; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006801:Humans; D007249:Inflammation / Q000097:blood*; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012907:Smoking / Q000097:blood; D019207:beta Carotene / Q000097:blood*
D015415:Biomarkers; D019207:beta Carotene; D002097:C-Reactive Protein