Excessive exposure to solar radiation, especially UVA (320-400 nm) and UVB (290-320 nm), may induce UV-carcinogenesis and erythema in the skin (Lee et al 2000). There have been a number of controlled clinical trials that have demonstrated that supplementation with beta-carotene alone, or in combination with other antioxidants, can reduce UV-induced erythema (Gollnick et al 1996, Heinrich et al 1998, 2003, Lee et al 2000, Mathews-Roth et al 1972, Sies & Stahl 2004, Stahl et al 2000). These studies suggest that at least 8-10 weeks of supplementation are required before protection against erythema becomes evident and that doses of at least 24 mg/day of beta-carotene are required (Sies & Stahl 2004).
In uncontrolled studies, a protective effect against UV-induced erythema was observed after supplementation with 180 mg of beta-carotene for 10 weeks (Mathews-Roth et al 1972) and 50 mg for 6 weeks (Heinrich et al 1998). These results are supported by more rigorous studies that have shown photoprotective activity with smaller doses of beta-carotene. A RCT involving supplementation with 30 mg of natural beta-carotene for 8 weeks, with the dose increasing to 60 mg for a further 8 weeks and then to 90 mg for another 8 weeks, found a dose-dependent reduction in UVA- and UVB-induced erythema (Lee et al 2000). In another RCT, supplementation for 12 weeks with 24 mg/day of natural beta-carotene or a natural carotenoid mix supplying similar amounts of beta-carotene, lutein and lycopene also significantly reduced UV-induced erythema (Heinrich et al 2003). Similarly, a randomised trial found that supplementation with 25 mg of natural algal beta-carotene for 12 weeks significantly reduced UV-induced erythema, with the effect enhanced by the addition of alpha-tocopherol (Stahl et al 2000). Yet another trial suggests that the photoprotective action of beta-carotene enhances the action of topical sunscreens. In this randomised, placebo-controlled, double-blind study of 20 healthy young females, 30 mg/day beta-carotene for 10 weeks reduced UV induced erythema and protected against UV-induced drop in serum beta-carotene levels and UV-induced reduction in Langerhans cells, with beta-carotene combined with topical sunscreens being more effective than sunscreen cream alone (Gollnick et al 1996). Another controlled study found a protective effect against photo-immunosuppression, with 30 mg/day of beta-carotene for 4 weeks protecting against UV-induced suppression of delayed-type hypersensitivity in young men (Fuller et al 1992).
It has been suggested that the duration of supplementation may be more important than the dose, as the studies that have not demonstrated significant reduction in UV-induced erythema have all involved supplementation of relatively Beta-carotene 95
short duration (Lee et al 2000). No photoprotective effects of beta-carotene were
observed with supplementation with 90 mg for 3 weeks (Garmyn et al 1995), 1 50 mg/day for 4 weeks (Wolf et al 1988) or 1 5 mg/day for 8 weeks (McArdle et al 2004).
It has also been suggested that a combination of antioxidants may be more effective than the sum of the separate components because the skin's antioxidant defence system appears to involve an intricate connection between individual antioxidants (Steenvoorden & Beijersbergen van Henegouwen 1997). This is supported by a randomised, double-blind, placebo-controlled study that found that short-term (2-week) supplementation with an anti-oxidative combination containing beta-carotene and lycopene, as well as vitamins Cand E, selenium and proanthocyanidins, significantly decreases the UV-induced expression of matrix metallo-proteinases, with a non-statistically significant trend towards reduced minimal erythema dose (Greul et al 2002).
Although beta-carotene supplementation may provide some degree of protection against sunburn, the effect is modest and there is still some debate about its use for routine photoprotection (Biesalski & Obermueller-Jevic 2001, Fuchs 1998). However, beta-carotene is likely to be clinically useful in providing photoprotection for people with specific photosensitivity. High doses (180 mg/day, up to 300 mg/day) have been shown to reduce photosensitivity in people with the genetic condition 'erythropoietic protoporphyria' in a number of case series (Mathews-Roth et al 1970, 1974, Thomsen et al 1979), and the results of a double-blind RCT suggest that beta-carotene may be useful in conjunction with canthaxanthin in preventing polymorphous light eruptions (Suhonen & Plosila 1981).
The ability of beta-carotene to protect against UV-induced erythema and photosensitivity does not appear to extend to protecting against non-melanotic skin cancer. In a randomised placebo-controlled trial involving 1805 subjects with recent non-melanotic skin cancer, daily supplementation with 50 mg beta-carotene for 5 years had no effect on the incidence of new or recurring non-melanotic skin cancers, with similar results for those with low baseline beta-carotene levels and smokers (Greenberg et al 1990). Similarly, in another randomised, placebo-controlled trial of 1621 adults aged 25-74 years daily supplementation with 30 mg beta-carotene did not reduce the development of solar keratoses over the 3-year study period (Darlington et al 2003, Green et al 1999). These results are supported by an analysis of data from the Physicians' Health Study that found no effect of 12 years of beta-carotene supplementation on the incidence of non-melanotic skin cancer
(Frieling et al 2000), as well as a subgroup analysis from this study that found no Beta-carotene 96
effect on non-melanotic skin cancer in men with low baseline plasma beta-carotene
levels (Schaumberg et al 2004). In a further randomised, placebo-controlled study of 62 patients with numerous atypical naevi, 25 mg of beta-carotene given twice daily for 36 months resulted in a non-significant reduction in newly developed naevi, with a significant reduction observed for the lower arm and feet but not for 10 other body sites (Bayerl etal 2003).
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