Alzheimer's disease (AD) is the most common form of neurodegenerative disorders leading to dementia. Currently, there has been no effective drugs targeting this disease. Functional food is considered as a potentially non-pharmacologic treatment. In this project, the investigators aim to investigate the effectiveness of a mixed functional food with main compositions of ginsenoside, green tea polyphenols and marine collagen peptide on cognition for individuals with subjective cognitive decline (SCD). Taking the randomized, double-blind, placebo-controlled method, participants in the functional food group will take mixed functional foods for three months and those in the placebo group will take placebo. After that, the investigators will investigate the changes of cognitive function. Furthermore, based on the neuroimaging technique, the regulatory mechanism of functional food in intervening SCD will be revealed from the perspective of altered brain functional activity. In conclusion, these results are beneficial for understanding the therapeutic effect of mixed functional foods as a non-drug treatment for early AD and further elucidating the potential brain mechanism, which are of great values in solving scientific and clinical practice issues.

Currently, there has been no effective therapy for Alzheimer's disease (AD). Functional food is now considered as a potentially non-pharmacologic intervention and supplementation of functional food may positively affect cognitive function for patients with AD. However, there are few existing studies involving the role of mixed functional foods with multiple compositions on cognition and neuroimaging biomarkers for subjective cognitive decline (SCD).

Sixty participants with SCD will be recruited in this three-month, randomized, double-blind, placebo-controlled trial. Each group had thirty participants. Participants in the functional food group will take mixed functional foods for three months and those in the placebo group will take placebo. After that, the investigators will investigate the changes of memory measures, which is the primary outcome. Furthermore, based on the neuroimaging technique of functional near-infrared spectroscopy (fNIRS), the regulatory mechanism of mixed functional foods in intervening SCD will be revealed from the perspective of altered brain functional activity.

In conclusion, these results are beneficial for understanding the therapeutic effect of mixed functional foods as a non-drug therapy for preclinical AD and further elucidating the potential brain mechanism, which are of great values in solving scientific and clinical practice issues.

Inclusion Criteria:

• 50-79 years old, right-handed and Mandarin-speaking subjects;
• self-experienced persistent decline in cognitive capacity in comparison with a previously normal status and unrelated to an acute event;
• normal age-adjusted, gender-adjusted and education-adjusted performance on standardised cognitive tests;
• concerns (worries) associated with memory complaint;
• failure to meet the criteria for MCI or dementia

Exclusion Criteria:

• a history of stroke;
• major depression (Hamilton Depression Rating Scale score > 24 points);
• other central nervous system diseases that may cause cognitive impairment, such as Parkinson's disease, tumors, encephalitis and epilepsy;
• cognitive impairment caused by traumatic brain injury;
• systemic diseases, such as thyroid dysfunction, syphilis and HIV;
• a history of psychosis or congenital mental growth retardation.

The information of neuropsychological tests, neuroimaging data are to be shared with other researchers.

When summary data are published or starting 6 months after publication.

The information of neuropsychological tests, neuroimaging data will be shared.