This study adapts a randomized, double-blind, placebo-controlled trial, to exam the possible benefit of Astaxanthin on Alzheimer disease. The enrolled Alzheimer patients will take Astaxanthin or placebo for 1 year. We will follow up Mini-Mental State Examination, Cognitive Ability Screening Instrument, Clinical Dementia Rating, and Neuropsychiatric Inventory at the end of the study.

This study aims to examine the benefit of Astaxanthin as adjuvant therapy for Alzheimer's disease.

Inclusion Criteria:

1. 60 ≦ age ≦ 90
2. Clinical Dementia Rating Scale = 0.5 or 1
3. Under treatment with donepezil、rivastigmine or galantamine with good medical adherence
4. Get a signed informed consent from the patient or his/her family

Exclusion Criteria:

1. Not using or poor medical adherence to donepezil、rivastigmine or galantamine
2. Combined using memantine or other cerebral perfusion enhancing agent, such as Piracetam, Dihydroergotoxine, Nicergoline etc.
3. New cerebrovascular disease happens during 3-year follow up
4. Mixed type dementia
5. Major psychiatric disease (such as depression, bipolar disorder, schizophrenia) or substance abuser (such as alcohol, illegal drug, hypnotics)
6. Heart failure, end stage renal disease, liver cirrhosis, or other major organ failure
7. Severe hearing impairment results in incomplete survey of neuropsychatric evaluation
8. No informed consent or no regular follow up

Will not share individual participant data