Table 4.

Human blood-brain barrier penetration by polyphenols.

Sample	Study Group	Analyzed Polyphenols	Polyphenols Detected in CNS	References
CSF *, plasma *	Twenty-eight patients (age 46 ± 16 years; 18 women and 10 men) with neurological diseases (multiple sclerosis, polyneuropathy, mononeuropathy, meningitis, brain tumor, epilepsy, amyotrophic lateral sclerosis, an Friedreich’s ataxia) on a “western” diet	vanillic acid dihydrocaffeic acid caffeic acid homovanillic acid 3-hydroxyphenyl acetic acid hippuric acid 3-hydroxyhippuric 4-hydroxyhippuric 3,4-dihydroxybenzoic acid chlorogenic acid ellagic acid urolithin A	caffeic acid homovanilic acid 3-hydroxyphenylacetic acid	[68]
CNS *	Six patients (aged 34–61, 3 women and 3 men) with suspicion of multiple sclerosis acute ingestion of green tea	(2)-epigallocatechin glucuronide (2)-epicatechin glucuronide (2)-epicatechin sulfate methyl-(2)-epicatechin sulfate	undetectable in the CSF	[120]
Brain MRI * CSF *	One hundred and nineteen patients with mild-to-moderate Alzheimer’s disease 52-week supplementation with resveratrol (500 mg/day, with a dose increase of 500 mg every 13 weeks, final dose 2000 mg/day)	resveratrol 3-O-glucuronidated-resveratrol (3GRES) 4-O-glucuronidated-resveratrol (4GRES) 3-sulfated-resveratrol (SRES)	resveratrol 3-O-glucuronidated-resveratrol (3GRES) 4-O-glucuronidated-resveratrol (4GRES) 3-sulfated-resveratrol (SRES)	[121]
CSF *	Thirty-six patients with mild-to-moderate Alzheimer’s disease oral curcumin supplementation at a dose of 2 g/day, 4 g/day, or placebo for 24 weeks, then for the next 24 weeks	tetrahydrocurcumin glucuronidated metabolites of curcumin	undetectable in the CSF	[122]
human brain tissue #		quercetin-3-O-glucuronide (Q3GA)	quercetin-3-O-glucuronide (Q3GA)	[123]

# postmortem sample; * samples taken while alive.