Beta-carotene research shows conflicting results; dose and duration questions remain

Beta-carotene research in particular indicates that dosage knowledge is far from complete, speakers told attendees of the conference held at The Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University on March 11-12, 2011.

Epidemiological studies and clinical trials often have vastly different or even opposite results, highlighting the difference between nutrient supplementation in the physiological and pharmacological ranges. While observational studies have suggested possible cancer-fighting effects of beta-carotene, for instance, only one major intervention trial has mirrored these effects, and the trial was done in a nutrient deficient population in rural Linxian County, China.

At last week’s conference, Dr. Susan T. Mayne, Division Head of Chronic Disease Epidemiology at the Yale School of Public Health, pointed to these studies and similar ones involving selenium, folic acid, and vitamin D to demonstrate that populations with low baseline serum levels of carotenoids might benefit from supplementation, but populations with a high baseline might not benefit and may even experience adverse effects.

The next generation of intervention trials should target nutrient-deficient populations before seeking external validity in broader populations, suggested Mayne. Additionally, future trials should take advantage of emerging rapid scan technology. Mayne and her colleagues recently published a paper in The American Journal of Clinical Nutrition​ (August​ 4, 2010​) validating the use of Resonance Raman spectroscopy - a quick, non-invasive dermal test - for measuring carotenoid levels in human skin.

Inconsistent science​

Data presented by Dr. Francine Grodstein, Associate Professor of Medicine at Brigham and Women's Hospital and Harvard Medical School, suggest inconsistencies in the realm of beta-carotene and cognitive function as well. The Women​’​s​​Antioxidant​​and​​Cardiovascular​​Study​, following the same pattern as the studies discussed by Mayne, showed some maintenance in cognition over nine years of a group with low baseline beta-carotene intake, but there were no significant results in women with high baseline intake.

The Physicians​’ ​Health​​Study​​II​, though, gave statistically significant (albeit modest) results across the board: Beta-carotene supplementation was correlated with a 1-2 year delay in cognitive aging over the course of the study, 1997-2007. An observational study, the Nurses​’ ​Health​​Study​, showed no relationship between total carotenoid intake and women’s cognitive decline over 20 years. The carotenoids were also analyzed individually; only lycopene intake was significantly correlated to cognition (particularly verbal memory).

Bioavailability​

While researchers continue to study the effective doses and durations of carotenoid supplementation, the enhancement of bioavailability is also useful puzzle to explore. Bioavailability can be influenced at three points in the manufacture of a supplement: the active ingredient, the product formulation, and the end product. These factors can influence product stability, which must be balanced carefully with bioavailability.

Dr. Bruno Leuenberger, corporate scientist for Nutrition Formulation & Application at DSM Nutritional Products, discussed the company’s Actilease beadlet as an example of a formulation with a good balance of stability and bioavailability. These beadlets are created through a two-step proccess: micronization of the carotenoid into a protective matrix, followed by drying. The resulting beadlets have a long shelf-life and high bioavailability: the matrix protects the nutrients while in storage and releases them in the body.