Astaxanthin is lipid soluble. The level of esterification determines astaxanthin's absorption in the digestive system. When astaxanthin is esterified, meaning bound to fat or ingested with oil, it is readily absorbed. Other factors that influence bioavailability include oxidation levels, chemical structure (isomerization and stereoisomerization), processing methods and raw material sources. 

The esterified form of Haematococcus pluvialis algae is extremely stable and displays high bioavailability and potency. The free-ester astaxanthin form is extremely sensitive to oxidation. 

Algatechnologies assessed the bioavailability of AstaPure® natural astaxanthin in humans1. Seven healthy volunteers were given 10 mg of AstaPure®. Astaxanthin levels were then measured in the blood. Results showed that astaxanthin levels increased steadily in the blood over 8 hours in all delivery forms, comparable to the absorption of other carotenoids. The study also found that AstaPure® absorbed well in the chylomicron fraction of the blood. 

1 Algatechnologies internal clinical study, 2011