There is currently no upper intake limit for vitamin B12.
Vitamin B12 Supplements
• Dosage. The most common dosages of vitamin B12 supplements are 500–1,000 mcg.
• Types. Two major types of vitamin B12 supplements are cyanocobalamin and methylcobalamin. The former is synthetic and the latter naturally produced. In the intestines, cyanocobalamin is converted to methylcobalamin in a two-step process. First, cyanide is removed from cyanocobalamin to produce cobalamin, and then cobalamin is methylated to produce methylcobalamin. In the process, cyanide is released from cyanocobalamin, and though it’s only a small amount, cyanide is a toxin. So methylcobalamin is safer than cyanocobalamin, even though the former is more expensive than the latter.
• Vegetarians. Vitamin B12 comes predominantly from animal-based foods, not from plant-based ones. Vegetarians should consider taking vitamin B12 supplementation at a dosage of 100 mcg daily or 700 mcg weekly.
• Elderly. Supplementation with vitamin B12 is recommended for individuals aged 60 and older, particularly for those who take antacid medications.
• Cognitive decline. Vitamin B12 may prevent age-related cognitive decline. The suggested daily dose is 100 mcg.
What Types of Drugs May Interact with Vitamin B12?
• Drugs like omeprazole, ranitidine, colchicine, and metformin reduce the absorption of vitamin B12 through the intestines.
Vitamin C is also known as ascorbic acid. Vitamin C deficiency causes scurvy. As early as 3000 BCE, a scurvy epidemic was recorded in Egypt. In 1753, James Lind demonstrated experimentally that fruit consumption could alleviate scurvy in sailors during a long sea voyage. In 1854, the English court enacted laws stipulating that all sailors during long sea voyages be given a daily portion of fruits. In 1928, Albert Szent-Györgyi isolated a six-member carbon compound from the adrenal gland, oranges, and cabbage. In 1932, his research group demonstrated that this water-soluble substance could cure scurvy, and they named it ascorbic acid. Szent-Györgyi was awarded the 1937 Nobel Prize in Physiology or Medicine for his contributions.
Some mammals—such as monkeys, cows, sheep, and dogs—can produce vitamin C in the body. They do not have to rely on foods for vitamin C. Humans cannot produce vitamin C because we do not have an enzyme in the liver required for the de novo synthesis of vitamin C; thus, we need to acquire it from plant-based foods.
Vitamin C is an electron donor, a chemical entity that donates electrons to another chemical entity. All functions of vitamin C in the body are related to this electron donor property. Vitamin C can donate electrons to at least 12 different enzymes that are responsible for many physiological functions. One of these enzymes is involved in the synthesis of collagen. Collagens are the major proteins in the skin, cartilage, tendons, ligaments, and blood vessels.
Vitamin C can also donate electrons to free radicals. After accepting electrons from vitamin C, free radicals are neutralized and can no longer harm the cell. Vitamin C protects DNA, proteins, and lipids in the cell from free radical–induced oxidative damage. Vitamin C participates in many other physiological functions, including accelerating wound healing, repairing and maintaining healthy bones and teeth, and enhancing iron absorption in the intestines.
What Are the Symptoms of Vitamin C Deficiency?
• Scurvy. Severe vitamin C deficiency causes scurvy, characterized by subcutaneous bleeding, hair and tooth loss, swollen joints, impaired wound healing, and even death. Nowadays, scurvy is a rare disease restricted only to a high-risk group that includes cancer patients with cachexia, a wasting syndrome in which patients lose weight and experience a decline in overall health and malnutrition. Alcoholics, drug abusers, and institutionalized elderly people are also especially vulnerable.
• Vitamin C insufficiency. Vitamin C insufficiency implies the blood level of vitamin C is insufficient, although it has not reached the deficient state. The symptoms of vitamin C insufficiency include dry and cracked hair, periodontal disease, easy bruising, nosebleed, and bacterial infections.
Prevention and Treatment of Diseases
• Prevention. Meta-analysis confirms that vitamin C can prevent breast cancer (47), renal cell cancer (100), bladder cancer (44), stomach cancer (107), cervical cancer (50), esophageal cancer (64), endometrial cancer (63), Alzheimer’s disease (37), gout (71), stroke (108), cervical intraepithelial neoplasia (51), cataracts (49), exercise-induced bronchoconstriction (65), atrial fibrillation (40), and sleep apnea (106).
• Treatment. Meta-analysis confirms that vitamin C can treat breast cancer (47), hypertension (78), cardiovascular disease (48), asthma (38), hemodialysis (75), sleep apnea (106), and hypercholesterolemia (77).
Can Vitamin C Prevent or Treat the Common Cold?
Can vitamin C prevent you from catching a cold? This is still an unsettled question, taking a vitamin C supplement seems to prevent athletes from catching a cold, but it will not protect nonathletes. However, taking a vitamin C supplement soon after catching a cold may alleviate cold symptoms and accelerate the recovery. The recommended daily dose is 1,000 mg of vitamin C.
Which Food Items Are Vitamin C Rich?
Plant-based foods, such as fruits and vegetables, are excellent sources of vitamin C. Fruits—including oranges, grapefruits, lemons, limes, papayas, strawberries, pineapples, cantaloupes, and raspberries—are rich in vitamin C. Vegetables—such as broccoli, kale, potatoes, sweet potatoes, tomatoes, bell peppers, and cauliflower—contain high amounts of vitamin C.
This list of vitamin C–rich food items is adapted from information provided by the USDA.
| FOOD | PORTION | VITAMIN C CONTENT, MG | % DAILY REFERENCE VALUE |
|---|---|---|---|
| Red bell pepper | ½ cup | 95 | 158 |
| Kiwi | 1 | 91 | 152 |
| Strawberry | 1 cup | 85 | 142 |
| Orange juice |
¾ cup
|
