Red grapes and blueberries both contain compounds that work with vitamin D to boost the immune system, research suggests.
In experiments, the plant compounds, called stilbenoids, increased activity of a gene involved in immune function.
Stilbenoids are produced by plants to fight infections. In humans, they appear to affect signalling pathways used by vitamin D.
Experiments showed combining the compounds with vitamin D made them much more potent. The stilbenoid in red grapes is resveratrol, which has already been hailed for its potential inflammation and cancer-fighting properties.
Its counterpart in blueberries is a compound called pterostilbene. The new findings are published in 'Molecular Nutrition and Food Research'.