Yes grapefruits are very healthy and full of vitamins and eating a grapefruit per day everyday is very healthy and can improve your health.
You can eat as many grapefruits as you want although you might eventually get tired of eating them over and over but it's not harmful at all to eat a grapefruit everyday if you want too.
The grapefruit will provide you with needed vitamins and nutrients and help boost your immune system as well.
Grapefruits are very rich in nutrients, antioxidants and fiber which makes grapefruits one of the healthiest citrus fruits in the world.
Grapefruits could also help ward off diseases including heart disease and possibly cancer.