Professor Spencer has published over 200 peer-reviewed papers, is Editor-in-Chief of Nutrition and Healthy Aging, and has been recognised as a highly cited researcher by the Institute for Scientific Information. His early research focused on the cellular and molecular mechanisms underlying neuronal death in Parkinson's and Alzheimer's disease.

He is currently researching how flavonoids and other dietary phenolics influence brain health, exploring their role in protecting against neurotoxins, promoting cerebrovascular blood flow, preventing neuroinflammation, supporting memory and cognitive performance. He also investigates the potential of flavonoid-rich foods to lower blood pressure and improve blood flow to the brain.