All vitamins are essential for a healthy diet, although some might be more vital to certain people at various life-stages. For example, vitamin A may be more important to elderly people experiencing visual problems, whereas vitamin C offers protective properties to smokers. In the United States, large segments of the population are chronically deficient in some vitamins, such as vitamin D. In general, vitamins from natural food sources are better assimilated by the body than supplements, which are often synthetically produced.
Vitamin A
Vitamin A, or retinol, is essential for healthy vision, strong immunity, vibrant skin and normal fetal development. It is an antioxidant able to scavenge free radicals and prevent them from damaging blood vessels and tissues. According to "Vitamins: Fundamental Aspects in Nutrition and Health," the recommended daily amounts are about 3,000 IU, with the upper safe limits set at 10,000 IU. Rich sources of retinol include the livers of beef, poultry and fish, eggs and most dairy products. Beta-carotene is converted to retinol in the liver and can be found in fleshy, orange vegetables such as carrots and sweet potatoes, but also in spinach, watercress, cantaloupe and mangoes. Deficiency of vitamin A leads to night blindness, dry eyes and skin conditions, such as dandruff, acne and eczema.
B Vitamins
The B vitamins are a collection of eight substances that are required for cellular metabolism, energy production and strong immunity. Of the group, vitamin B-9, or folic acid, is especially important during pregnancy and for normal fetal growth. Vitamin B-6, or pyridoxine, is also able to reduce prolactin levels in men, which reduces the risks of benign prostate enlargement, according to "Human Biochemistry and Disease." Vitamin B-12, or cobalamin, is essential for the health of sperm cells, as deficiency results in reduced motility and count. Vitamin B-12 also enhances cognition and memory retention, which might help combat the progression of Alzheimer's disease. The B vitamins are often found together in the same foods, such as beef, organ meats, dairy products, eggs, fish, poultry, nuts, legumes and green leafy vegetables, such as spinach.
Vitamin C
Vitamin C, or ascorbic acid, is required for strong immunity, and production and maintenance of connective tissue. Vitamin C naturally lowers blood cholesterol levels and strengthens blood vessels, which contributes to reduced risk of cardiovascular disease, according to the Linus Pauling Institute. Recommended daily amounts of vitamin C are 90 mg for adult males, although Dr. Pauling recommended at least 1,000 mg daily for children and adults. Rich sources of vitamin C include citrus fruits, especially lemons, rose hips, kiwis, strawberries, guava, peppers, Brussels sprouts and broccoli.
Vitamin D
Vitamin D is essential for strong immunity and healthy bones. The best source is sunshine, as UV-B radiation causes the formation of cholecalciferol within the skin. According to "Nutrition and Public Health," up to 75 percent of Americans are vitamin D deficient, which is mainly due to indoor lifestyles, fear of skin cancer and use of sunscreens. Deficiency symptoms include fatigue, achy muscles and sore joints, among others. Recommended daily levels range between 200 and 800 IU, depending on age and gender, although exposed light-colored skin can produce 10,000 IU in 20 minutes under ideal conditions. Rich sources of vitamin D include fatty fish, such as salmon and mackerel, beef liver, egg yolks and fortified cereals, dairy products and orange juice.
References
- "Vitamins: Fundamental Aspects in Nutrition and Health"; G. Combs; 2008
- "Human Biochemistry and Disease"; Gerald Litwack; 2008
- Linus Pauling Institute, Oregon State University: Vitamin C
- "Nutrition and Public Health"; Sari Edelstein; 2006
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