Bioflavonoids contained in lemon have antioxidant effects and are thought to be responsible for the beneficial effects of lemon. Coumarins found in lemon appear to reduce free radical generation by inhibiting the product of nitric oxide thus acting as an antioxidant. In animal models of diabetes, a diet containing lemon flavonoids consisting of 0.2% eriocitrin and 0.2% hesperidin results in reduced measures of oxidative stress after 28 days of treatment.
For kidney stones, lemons, lemon juice, and lemonade are used due to the citric acid content of lemon. Citrate inhibits the formation of calcium-based kidney stones. Consuming lemon products seems to increase urinary citrate levels. Theoretically, this might result in decreased incidence of calcium kidney stone formation. There is interest in potential anticancer activity of citrus flavonoids, including those found in lemon. Other benefits that have not been studied but have been used throughout history include, overcoming nausea, motion sickness and indigestion. Whether lemon juice in hot water directly leads to weight loss as many websites purport, it has not been proven in published, scientific research. On another side note, many people add lemon slices or juice to their water to make it more refreshing.