Water-soluble vitamin C is neither made by humans nor stored for long in our systems. Vitamin C moves quickly through our bloodstreams and is excreted through urine.

For this reason, we need to constantly replenish our vitamin C supply by eating foods rich in the nutrient, such as citrus fruits, strawberries, broccoli, peppers and spinach.

Supplements and multivitamins can also increase intake, but there's no need to overload on this well-known antioxidant, as recommended daily intake varies from person to person. For example, smokers need more vitamin C than non-smokers.

Vitamin C protects cells from free radical damage and helps strengthen weakened immune systems. It also helps increase iron absorption and bioavailability.

For example, if you add grapefruit slices to your spinach salad, the vitamin C will help release the iron from the spinach for the body to use.

A member of the citrus family with a strong nutritional profile. High in vitamin C, one-half grapefruit includes 70 percent of the daily recommended allowance of this valuable vitamin.

Grapefruit's sweet, tart, and sour qualities come from various phytochemicals that also act as cancer-fighters in the body. Winter is citrus season, and these fruits are usually lower in price and higher in quality this time of year.

Try them at breakfast or as a mid-morning snack, or combine grapefruit segments with avocado and spinach for a delightful winter salad.