Dietary Reference Intakes, antioxidants, and beta carotene

Association between β-carotene supplementation and risk of cancer: a meta-analysis of randomized controlled trials

CONTEXT

β-Carotene, which is derived from most fruits and vegetables, is the most common type of carotenes. Existing studies have demonstrated that β-carotene is associated with some positive health outcomes. However, results about the effects of supplemental β-carotene on cancer are inconsistent.

OBJECTIVE

To determine the association between supplemental β-carotene intake and the risk of cancers.

DATA SOURCES

Eight databases (PubMed, Web of Science, Embase, Cochrane, China National Knowledge Infrastructure, Wangfang, China Science and Technology Journal Database, and Chinese Biomedical Literature Database) were systematically searched until September 2022.

DATA EXTRACTION

Only reports from randomized controlled trials in which an association between supplemental β-carotene intake and the risk of cancer was found were included in the meta-analysis.

DATA ANALYSIS

A total of 18 eligible studies based on 8 different randomized controlled trials were included in the meta-analysis, with varying sample sizes from 391 to 39 876 participants. There was no significant association between supplemental β-carotene intake and overall cancer incidence rate after synthesizing all the results (risk ratio [RR]: 1.02; 95% confidence interval [CI], 0.99-1.05). Results from subgroup analysis indicated that intake of supplemental β-carotene significantly increased the risk of lung cancer (RR: 1.19; 95%CI: 1.08-1.32), whereas no significant associations were observed for other site-specific cancers. In addition, smokers and the subgroup of participants with only low-dose β-carotene intake had a risk increment of cancer if they took supplemental β-carotene (RR: 1.16; 95%CI: 1.05-1.29).

CONCLUSION

β-Carotene supplementation has no beneficial or harmful effect on cancer incidence; moreover, it might have potentially harmful effects on lung cancer, especially for people who smoke. On the basis of the evidence from this study, supplemental intake of β-carotene is not recommended for preventing cancer, and the establishment of a tolerable upper intake level of β-carotene should be considered.

The intake of carotenoids in an older Australian population: The Blue Mountains Eye Study

OBJECTIVE

To describe the distribution of carotenoid intakes and important food sources of carotenoids in the diet of a representative population of older Australians.

DESIGN

Population-based cohort study.

SETTING

Two post-code areas in the Blue Mountains, west of Sydney, Australia.

SUBJECTS

We studied 2012 (86%) of the 2334 participants aged 55+ years attending the 5-year follow-up of the cross-sectional Blue Mountains Eye Study (BMES), who completed a detailed semi-quantitative food-frequency questionnaire. The intakes for five carotenoids were studied: alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein and zeaxanthin combined, and lycopene.

RESULTS

The mean intake per day for each carotenoid was: alpha-carotene, 2675 microg; beta carotene equivalents, 7301 microg; beta-cryptoxanthin, 299 microg; lutein and zeaxanthin, 914 microg; lycopene, 3741 microg; retinol, 653 microg; total vitamin A, 1872 microg retinol equivalents. beta-Carotene equivalents contribute a substantial proportion of total vitamin A intake (65%) in this population. Women had slightly higher intakes than men for alpha-carotene, beta-carotene equivalents, and lutein and zeaxanthin (P < 0.05). Carrots and pumpkin were the main contributors to alpha-carotene and beta-carotene equivalent intakes. Orange juice, oranges and papaw were the main contributors to beta-cryptoxanthin intake. Broccoli, green beans and oranges contributed substantially to lutein and zeaxanthin intake. The main contributors to lycopene intake were tomatoes and bolognaise sauce.

CONCLUSIONS

Vitamin A intake in this population is high relative to the Australian Recommended Dietary Intake. Carotenoid intakes, particularly beta-carotene, make a substantial contribution, particularly from fruit and vegetables. This study provides important information as a basis for examining associations between dietary carotenoid intake and eye disease in the BMES.