Minerals abound in watermelon seeds. Magnesium is the most abundant mineral, weighing in with 556mg, or 139 percent of the recommended daily value, in 1 cup of dried seeds. According to the National Institutes of Health, magnesium helps regulate blood pressure and the metabolism of carbohydrates, which has a beneficial effect on blood sugar as well. Other important minerals in watermelon seeds are phosphorous, iron, potassium, sodium, copper, manganese and zinc.