Title: Systematic review and meta-analysis on the effects of astaxanthin on human skin ageing

Abstract

Skin ageing is becoming a global challenge due to longer human longevity and intensive ultra-violet rays contributed to the ozone layer destruction, attracting greater scientific interests in developing nutricoesmetic products, especially from natural functional ingredients with lower side-effects. Astaxanthin, a carotenoid with high antioxidant and anti-inflammatory effects, prevented animal skin photoaging and age-related skin diseases. It could be extracted from the microalgae Haematococcus pluvialis and byproduct of processed crustaceans which are generally discarded as marine waste, losing potentially valuable ingredients, and causing serious environmental problems by accumulating high amounts of organic materials. This paper evaluated whether astaxanthin has cosmeceutical potential to prevent or reverse human skin ageing. A comprehensive search of PubMed, Scopus and Web of Science found a total of eleven studies. Nine randomised, controlled human studies assessed oral ASX effects and two open-label, prospective studies evaluated topical, oral-topical ASX effects on skin ageing. GetData Graph Digitizer was used to extract mean values and standard deviations of baseline and endpoint, and Cochrane Collaboration’s tool assessed RoB for all included studies. Review Manager 5.4 was used to conduct meta-analysis of RCTs; the results were reported as effect size ± 95% confidence interval. Continuous oral astaxanthin applications might restore moisture content, improve elasticity significantly, but did not significantly reduce wrinkle depth compared to the placebo group. Oral supplementations might be more sustained and pronounced than topical applications. A synergistic skin protective effect was found in the combinational usages in open-label-prospective studies. But the reliability of evidence was limited by small sample sizes, imperfect study design, and potential conflicts of interests, requiring more large-scale and robust studies to reconfirm the mechanisms. This paper clarifies the human skincare effects of astaxanthin and confirms its promising cosmetical potential, facilitating marine waste recycling, environmental protection, and sustainable development.