Testosterone levels in both men and women decline with age, and low testosterone levels have been related to memory problems. Studies have shown that low testosterone levels have preceded cognitive impairment and the neuropathology of Alzheimer’s, indicating it may be more of a cause than a consequence of the disease. The relationship between testosterone replacement therapy in men and women has been harder to quantify due in part to the small number of long-term, controlled studies available.

Another factor critical to brain function is omega-3 fatty acids, including DHA and EPA which usually come from fish oil. In the brains of older people, there is a depletion of long chain omega-3 fatty acids, and those with Alzheimer’s disease have lower DHA levels. DHA supplements can reduce markers of inflammation, which may influence Alzheimer’s disease. In dietary intervention studies, supplementation with DHA and/or EPA seems to be more effective in improving cognition in early stages of cognitive impairment.

Research on the impact of testosterone and dietary supplements is complex and studies frequently report conflicting results.  This may be due to the many individual factors that can affect outcomes, brief follow up, different methods, and lack of comparable imaging data. Long-term randomized clinical trials are needed before conclusions can be made.

To help understand the influence of testosterone and fish oil for Alzheimer’s disease and memory, the Parsemus Foundation provided early support for a randomized controlled prospective trial on the impact of testosterone or DHA versus placebo on the onset of amyloid plaque associated with Alzheimer’s disease in men with memory complaints. The study is being conducted at Alzheimer’s Research Australia (formerly called the McCusker Alzheimer’s Research Foundation). Based on the results of a smaller non-placebo trial, the researchers led by Dr. Ralph Martins are optimistic that one or both treatments may slow the development of amyloid plaque and cognitive decline.

The trial has been screening men by completing a positron emission tomography (PET) amyloid scan prior to selection for the trial. The enrollment for the trial has ended in 2025 with participants undergoing completion of the study. In addition to the treatment arms, blood tests and retinal images from all participants will help to develop early diagnostic tests for Alzheimer’s disease.

Learn more about dementia and Alzheimer’s disease — and what you can do to lower your risk. There are many lifestyle changes that can reduce the chance of developing Alzheimer’s disease, such as diet, exercise, and appropriate supplements. See Additional Resources below.

Last updated on March 12, 2025