In addition to their possible direct biological effects, plasma carotenoids can be used as biochemical markers of fruit and vegetable consumption for identifying diet–disease associations in epidemiological studies. Few studies have compared levels of these carotenoids between countries in Europe.

Our aim was to assess the variability of plasma carotenoid levels within the cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC).

Plasma levels of six carotenoids – α-carotene, β-carotene, β-cryptoxanthin, lycopene, lutein and zeaxanthin – were measured cross-sectionally in 3043 study subjects from 16 regions in nine European countries. We investigated the relative influence of gender, season, age, body mass index (BMI), alcohol intake and smoking status on plasma levels of the carotenoids.

Mean plasma level of the sum of the six carotenoids varied twofold between regions (1.35μmoll−1 for men in Malmö, Sweden vs. 2.79μmoll−1 for men in Ragusa/Naples, Italy; 1.61μmoll−1 for women in The Netherlands vs. 3.52μmoll−1 in Ragusa/Naples, Italy). Mean levels of individual carotenoids varied up to fourfold (α-carotene: 0.06μmoll−1 for men in Murcia, Spain vs. 0.25μmoll−1 for vegetarian men living in the UK). In multivariate regression analyses, region was the most important predictor of total plasma carotenoid level (partial R2=27.3%), followed by BMI (partial R2=5.2%), gender (partial R2=2.7%) and smoking status (partial R2=2.8%). Females had higher total carotenoid levels than males across Europe.

Plasma levels of carotenoids vary substantially between 16 different regions in Italy, Greece, Spain, France, Germany, the UK, Sweden, Denmark and The Netherlands. Compared with region of residence, the other demographic and lifestyle factors and laboratory measurements have limited predictive value for plasma carotenoid levels in Europe.

To investigate the usefulness of serum carotenoids as biomarkers of fruit and vegetable consumption.

Reproducibility study on three repeat measurements of serum carotenoids. Correlation analysis of carotenoids and dietary food intake, and regression analysis of potential predictive parameters for serum carotenoid levels.

New York, USA.

Women participating in the New York Women's Health Study, a prospective study of sex hormones, diet and breast cancer. Forty-eight women with three repeat blood samples and 302 women having a blood sample and a dietary history questionnaire.

Serum carotenoid concentrations were highly reproducible between one- and two-year repeat samples. Estimated fruit and vegetable consumption was positively correlated with serum carotenoid concentrations but correlation coefficients were low. Consumption of fruit was predictive for serum levels of beta-carotene, alpha-carotene and beta-cryptoxanthin, while vegetable consumption was predictive for serum beta-carotene, lutein, zeaxanthin and lycopene. Serum concentrations of cholesterol and triglycerides were predictive for serum carotenoids but adjustment for their levels had little or no influence on the correlation between fruit and vegetable consumption and serum carotenoid concentrations.

One single serum measurement of alpha-carotene, beta-carotene and lutein can accurately rank subjects according to their usual serum level. Serum concentrations, however, correlate only moderately with estimated dietary intake of fruits or vegetables and should therefore be used with caution as biomarkers of fruit and vegetable intake.