Supplements

Vitamin C (ascorbic acid) is a vitamin your body needs to form blood vessels, cartilage, muscle and collagen in bones. Vitamin C is also vital to your body's healing process.

An antioxidant, vitamin C might help protect your cells against the effects of free radicals — molecules produced when your body breaks down food or is exposed to tobacco smoke and radiation. Free radicals might play a role in heart disease, cancer and other diseases. Vitamin C also helps your body absorb and store iron.

Because your body doesn't produce vitamin C, you need to get it from your diet. Vitamin C is found in citrus fruits, berries, potatoes, tomatoes, peppers, cabbage, Brussels sprouts, broccoli and spinach. Vitamin C is also available as an oral supplement, typically in the form of capsules and chewable tablets.

People with gastrointestinal conditions and some types of cancer might be susceptible to vitamin C deficiency. Vitamin C is also used to increase iron absorption from the gastrointestinal tract. Severe vitamin C deficiency can lead to a disease characterized by anemia, bleeding gums, bruising and poor wound healing (scurvy). If you take vitamin C for its antioxidant properties, keep in mind that the supplement might not offer the same benefits as naturally occurring antioxidants in food.

The recommended daily amount of vitamin C for adult men is 90 milligrams and for adult women is 75 milligrams.

Research on the use of vitamin C for specific conditions shows:

• Cancer. Eating a diet rich in fruits and vegetables might lower your risk of many types of cancer, such as breast, colon and lung cancers. However, it's not clear whether this protective effect is related to the vitamin C content in the food. Taking oral vitamin C supplements doesn't appear to offer the same benefit.
• Common cold. Taking oral vitamin C supplements won't prevent the common cold. However, there's some evidence that when people who regularly take vitamin C supplements get a cold, the illness lasts fewer days and symptoms are less severe. Starting a vitamin C supplement only after you develop a cold is of no help.
• Eye diseases. Taking oral vitamin C supplements in combination with other vitamins and minerals seems to prevent age-related macular degeneration (AMD) from worsening. Some studies also suggest that people who have higher levels of vitamin C in their diets have a lower risk of developing cataracts.

Most people get enough vitamin C from a balanced diet. However, people with gastrointestinal conditions and some types of cancer might be susceptible to vitamin C deficiency and benefit from the use of oral supplements. Taking vitamin C supplements also might have other protective benefits.

When taken at appropriate doses, oral vitamin C supplements are generally considered safe. Side effects tend to be dose-related. Oral vitamin C supplements can cause:

• Nausea
• Vomiting
• Heartburn
• Inflammation that might damage the esophagus (esophagitis)
• A blockage that keeps food or liquid from passing through your small intestine or large intestine (intestinal obstruction)
• Stomach cramps
• Fatigue
• Headache
• Sleepiness
• Diarrhea
• Insomnia
• Skin flushing
• 
  

In some people, oral use of vitamin C can cause kidney stones. Long-term use of oral vitamin C supplements over 2,000 milligrams a day increases the risk of significant side effects.

Tell your doctor that you're taking vitamin C supplements before having any medical tests. High levels of vitamin C might interfere with the results of certain tests, such as stool tests for occult blood or glucose screening tests.

Possible interactions include:

• Aluminum. Taking vitamin C can increase your absorption of aluminum from medications containing aluminum, such as phosphate binders. This can be harmful for people with kidney problems.
• Chemotherapy. There is concern that use of antioxidants, such as vitamin C, during chemotherapy might reduce the drug's effect.
• Estrogen. Taking vitamin C with oral contraceptive or hormone replacement therapy might increase your estrogen levels.
• Protease inhibitors. Oral use of vitamin C might reduce the effect of these antiviral drugs.
• Statins and niacin. Taking vitamin C with niacin, which might benefit people with high cholesterol, could reduce niacin's effect.
• Warfarin (Coumadin, Jantoven). High doses of vitamin C might reduce your response to this anticoagulant

Vitamin B-12 (cobalamin) is a water-soluble vitamin that plays essential roles in red blood cell formation, cell metabolism, nerve function and the production of DNA.

Food sources of vitamin B-12 include poultry, meat, fish and dairy products. Vitamin B-12 is also added to some foods and is available as an oral supplement. Vitamin B-12 injections or nasal spray might be prescribed to treat vitamin B-12 deficiency.

Because your body is capable of storing several years' worth of vitamin B-12, deficiency is rare. However, if you follow a vegetarian or vegan diet, you might be prone to deficiency because plant foods don't contain vitamin B-12. Older adults and people with digestive tract conditions that affect absorption of nutrients also are susceptible to vitamin B-12 deficiency.

Left untreated, a vitamin B-12 deficiency can lead to anemia, fatigue, muscle weakness, intestinal problems, nerve damage and mood disturbances.

The recommended daily amount of vitamin B-12 for adults is 2.4 micrograms.

Research on the use of vitamin B-12 for specific activities and conditions shows:

• Heart and blood vessel disease. Vitamin B-12, in combination with vitamin B-6 and folate (vitamin B-9), has been shown to control high levels of homocysteine in the blood. Elevated homocysteine might increase your risk of diseases of the heart and blood vessels (cardiovascular disease). Despite this benefit, there's no evidence to show that vitamin B-12 supplements prevent heart disease.
• Dementia. Vitamin B-12 deficiency is associated with dementia and low cognitive function, but it's not clear whether vitamin B-12 supplements might help prevent or treat dementia.
• Athletic performance. Unless you have a vitamin B-12 deficiency, there's no evidence that vitamin B-12 supplements will boost your energy or make you a better athlete.

Most people get enough vitamin B-12 from a balanced diet. However, older adults, vegetarians and people who have conditions that affect their ability to absorb vitamin B-12 from foods might benefit from the use of oral supplements.

Vitamin B-12 supplements also are recommended for women who are pregnant or breast-feeding exclusively and follow vegetarian or vegan diets.

When taken at appropriate doses, vitamin B-12 supplements are generally considered safe. While the recommended daily amount of vitamin B-12 for adults is 2.4 micrograms, you can safely take higher doses. Your body absorbs only as much as it needs, and any excess passes through your urine.

High doses of vitamin B-12, such as those used to treat a deficiency, might cause:

• Dizziness
• Headache
• Anxiety
• Nausea
• Vomiting

Possible interactions include:

• Aminosalicylic acid. Taking this drug used to treat digestive problems might reduce your body's absorption of vitamin B-12.
• Colchicine (Colcrys, Mitigare). Taking this anti-inflammatory drug used to prevent and treat gout attacks might decrease your absorption of vitamin B-12.
• Metformin (Glumetza, Glucophage, Fortamet). Taking this diabetes drug might reduce your absorption of vitamin B-12.
• Proton pump inhibitors. Taking omeprazole (Prilosec), lansoprazole (Prevacid) or other stomach acid-reducing drugs might decrease your absorption of vitamin B-12.
• Vitamin C (ascorbic acid) supplements. Taking vitamin B-12 with vitamin C might reduce the available amount of vitamin B-12 in your body. To avoid this interaction, take vitamin C two or more hours after taking a vitamin B-12 supplement.