You know you need to eat fruits because they contain nutrients that help keep you healthy. But if you don't eat your fruit soon after it's been picked, you may be losing out on some of the goodness. Vitamins, such as vitamin C, are susceptible to light and heat. While you may be eating that kiwi to help meet 100 percent of your daily value for vitamin C needs, if the kiwi has been sitting around for a few weeks, you may not be getting as much as you think.
Vitamin C is an essential water-soluble vitamin. As a water-soluble vitamin, any excess vitamin C you consume is excreted in your urine. This also means that vitamin C is not stored in your body and must be consumed regularly to meet your needs. Vitamin C is needed for the synthesis of collagen, a protein that helps with wound healing. Vitamin C also supports immune health and normal growth and development. It is also an important antioxidant, protecting your cells against oxidation, and decreasing your risk of chronic diseases such as cancer and heart disease. Your daily vitamin C needs vary depending on your age and gender. Adult men need 90 mg of vitamin C a day, and adult women need 75 mg a day, according to the Office of Dietary Supplements.
Stability of Vitamins
Vitamins are not stable substances, and are susceptible to destruction by heat, light, water, radiation or changes in acidity. Vitamin C is especially unstable, according to a report on ABC News, and can degrade through heat, oxidation -- or exposure to oxygen -- or alkaline conditions. Storage also destroys vitamin C, according to the authors of "Krause's Food, Nutrition and Diet Therapy."
Vitamin C Overtime
Over time, the vitamin C content of fruits decreases. A 2002 study published in the "Journal of the American Dietetic Association" compared the vitamin C content in fresh and reconstituted orange juice over a four- to five-week period. The vitamin C in the reconstituted orange juice decreased from 84 mg per 1-cup serving to 39 to 46 mg per 1-cup serving during the four-week study period. The vitamin C in the fresh orange juice decreased from 27 to 65 mg of vitamin C per 1-cup serving to zero to 25 mg per 1-cup serving.
While the study looks only at juice, vitamin C content in fruits are also affected, according to ABC News. To maximize the nutritional quality of your fruit and your intake of vitamin C, it is recommended that you purchase your fruit daily. Or, only purchase the amount of fresh fruit you can consume in three to four days. You may also consider frozen fruits as an option to maximize the vitamin C content of your fruit. The amount of vitamin C in frozen fruit remains stable over time.