How We Deal with Vitamin Deficiency and Overdose

By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital

Vitamins are crucial to a nutritional diet, but too much or too little of each can lead to serious health problems. Which foods provide the best sources of vitamins, how much is recommended of each and what happens when we stray from the recommended doses?

Every vitamin is associated with a deficiency syndrome, which is how they were first discovered. But, many of them are associated with known and sometimes serious overdose syndromes too.

Vitamin A

The RDA stands for the recommended daily allowance. Essentially, the RDA is the minimum amount you need to get of a vitamin daily to prevent a deficiency syndrome. The RDA for vitamin A is 900 micrograms. Deficiency causes night blindness. An overdose causes what we call hypervitaminosis A, which is a serious medical condition that can ultimately be fatal. Common sources of vitamin A include fruits and vegetables like mango, broccoli, carrots, spinach, and beef liver.

Learn more about where you can find Vitamin A in the foods you eat

B Vitamins

Next, we have B vitamins. Many B vitamins begin with B1 or thiamine. Here, the RDA is 1.2 milligrams. A deficiency of thiamine can cause a serious neurological disorder called Wernicke-Korsakoff syndrome where, in the end stage, people completely lose their short-term memory. Overdoses will tend to cause drowsiness. Common sources of thiamine include spinach, green peas, tomatoes, watermelon, sunflower seeds, and other vegetables.

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Another common form is B2 or riboflavin, with an RDA of 1.3 milligrams. The deficiency syndrome is ariboflavinosis, which causes changes to the skin and the oral mucosa—sores and bleeding, for example. Common sources include spinach, broccoli, mushrooms, eggs, milk, liver, and some seafood items like oysters and clams.

There is reasonable evidence to support that vitamin B2 reduces the frequency of migraine attacks. Therefore, in people with mild to moderate migraine headaches, supplementing B2 may improve the number of headaches that you have.

B3 or the niacin group has an RDA of 16 milligrams. A deficiency causes a syndrome that has been recognized for centuries called pellagra. We remember this by the three Ds—dementia, diarrhea, and dermatitis. Overdose can cause liver damage. Common sources include vegetables like spinach, also potatoes, tomato juice, lean ground beef, chicken breast, and tuna.

B5, or the pantothenic acid group, has an RDA of 5 milligrams. A deficiency causes paresthesia; that’s a tingling sensation in the nerves. It’s a mild form of nerve damage. Overdoses can cause nausea and diarrhea. As B5 is common in many foods, it’s difficult to become deficient in it.

Next in the family is B6 or pyridoxine. The RDA there is 1.3 milligrams. Deficiency of B6 causes anemia or low blood counts and also neuropathy or nerve damage. Ironically, overdoses of B6 also can cause nerve damage or neuropathy. Common sources include bananas, watermelon, tomato juice, broccoli, spinach, acorn squash, potatoes, rice, and chicken breast.

There’s evidence to support vitamin B6 for nerve healing. For those who have, for example, carpal tunnel syndrome—a common compression of the median nerve in the wrist—long-term healing and outcomes will be better if you take moderate supplements of vitamin B6. However, use caution; even slightly overdosing on B6 can cause nerve damage, thus, be sure you’re taking the proper dose.

B7 or biotin has an RDA of 30 micrograms. Deficiency causes dermatitis and dementia. It is also a vitamin that is common in many foods.

B9 or folic acid has an RDA is 400 micrograms. Deficiencies of folic acid are most important in pregnant women where they can cause a serious neurological developmental disorder called neural tube defects, such as spina bifida. Pregnant women should definitely take folic acid. Deficiencies in other populations can also cause anemia. Sources include tomato juice, green beans, broccoli, spinach, asparagus, black-eyed peas, and lentils.

Learn more about the most familiar B vitamins

B12 or cyanocobalamin has an RDA of 2.4 micrograms. A deficiency causes megaloblastic anemia—a low blood count of a specific type that can be diagnosed simply by doing a blood test. Common sources include meats, poultry, fish, shellfish, milk, and eggs.

Vitamin C

One of the next major vitamins is vitamin C or ascorbic acid. The RDA is 90 milligrams. Deficiencies cause scurvy, but this can be prevented with common sources of fruits and vegetables such as spinach, broccoli, red bell peppers, snow peas, tomato juice, kiwi, mango, orange, and surprisingly, there are high levels in strawberries.

It’s been long recognized that vitamin C is important for wound healing, as it is important for making structural proteins, the kind of things that hold our cells and tissue together. Therefore, if you’ve just had surgery or if you’re healing from an injury, taking extra vitamin C for a while will help you heal faster.

Learn more about whether Vitamin C can protect you from the common cold

Vitamin D

Vitamin D, or the cholecalciferols, have an RDA of five to 10 micrograms. A deficiency of vitamin D is called rickets, a condition that has been known for several centuries—longer than we’ve known about vitamin D—that causes abnormalities in bone development.

The most common source of vitamin D is simple sunlight. Most people can get all the vitamin D they need just from everyday exposure to the sun. However, vitamin D is also fortified in milk and can also be found in egg yolks, liver, and fatty fish.

Learn more about how Vitamin D plays a role in combating diseases

Vitamin E

Vitamin E, or the tocopherols, have an RDA of 15 milligrams per day. Deficiencies can cause neuropathy and ataxia, which is poor coordination or poor ability to walk. Common sources include nuts, oils, sunflower seeds, whole grains, wheat germ, and spinach.

Vitamin K

Finally, we have vitamin K or menaquinones and phylloquinones. They have an RDA of 120 micrograms.

A deficiency of vitamin K causes bleeding because vitamin K is important in the clotting cascade, the sequence of biochemical reactions that allows your blood to clot off and to stop bleeding from occurring. You can find vitamin K in the dark green, leafy vegetables including brussels sprouts, spinach, broccoli, kale, and liver.

Common Questions About Vitamin Deficiency and Overdose

This article was updated on September 9, 2020

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