Even if you have a glass of orange juice and take a multivitamin every day, you might still need more vitamin C. Here's why:
1. Low vitamin C is very common. One in three Americans has low blood levels of C. Researchers at Arizona State University think one reason is that foods don't contain as much vitamin C as we think. For example, orange juice in ready-to-drink cartons has far less C than juice from frozen concentrate.
2. The recommended daily allowance (RDA) for vitamin C is too low. C is an antioxidant superpower that neutralizes free radicals that are associated with cancer, heart disease, cataracts, and other conditions. According to physicians writing for Prevention, 500 to 1,000 mg of vitamin C per day are needed to saturate blood and tissue. Current RDA levels are 90 for men and 75 for women.
3. If you have diabetes, extra vitamin C is recommended. People with diabetes have high levels of oxidative stress, which can lead to blindness, nerve damage, and heart disease. Vitamin C helps to counter these effects. If you take supplements, be sure to tell your doctor.
The safe upper limit for vitamin C taken daily is 2,000 mg. Higher doses can cause diarrhea or stomach upset.
The American Cancer Society's committee on nutrition and physical activity says extra vitamin C isn't for everyone. Don't take it if you are taking chemotherapy. If your body stores excess iron, or if you have a history of kidney stones, don't take more than 100 to 200 mg per day.