Can Our Bodies Make Our Own Vitamins?

Vitamins are substances needed by everybody in small amounts to stay healthy. The human body can make its own vitamin D in the skin when it is exposed to sunlight, and friendly bacteria in the gut provide small amounts of vitamin K. Animals can make their own vitamin C, though unfortunately humans cannot. People need to get all the rest of the required vitamins from eating a healthy, balanced and varied diet.

Vitamin D

The only vitamin that the human body can make on its own is vitamin D. The action of the sun on the skin turns a compound called 7-dehydrocholesterol into a form of vitamin D called vitamin D3 (cholecalciferol). According to the Mayo Clinic in the USA, about 15 minutes of sun exposure on the skin a couple of times a week is enough to create the required levels of vitamin D. Vitamin D helps the absorption of calcium and maintains healthy bones and teeth (see 'Vitamin D').

People who do not get enough sun exposure, for example people who are bedridden, who have to keep entirely covered up outside for cultural or religious reasons, or who have dark skins but live in northern climates (especially during the winter) can find their levels of vitamin D dropping too low.

According to the World Health Organisation, adults need an average of 5-10 mcg of vitamin D daily, though the body can store this for a while, as vitamin D is a fat-soluble vitamin. Good food sources of vitamin D include oily fish, eggs and dairy.

Vitamin K

While the human body cannot make vitamin K on its own, the friendly bacteria in the gut can make vitamin K2 (menaquinone or menatetrenone). People on high doses of antibiotics can become deficient in vitamin K, because the drugs destroy the friendly gut bacteria. Doctors give newborn babies injections of vitamin K, as their guts have not yet been colonised with the right friendly bacteria.

Vitamin K is important to help blood clotting (see ‘Other Vitamins’), and may also be needed to keep bones strong and healthy. According to the World Health Organisation, adults need an average of 55-65 mcg of vitamin K daily, though the body can store this for a while, as vitamin K is a fat-soluble vitamin. Good food sources of vitamin K include vegetable oils, green leafy vegetables and wholegrains.

Vitamin B3 (niacin)

Many animals, including humans, can convert the amino acid tryptophan (found in foods rich in protein) to vitamin B3. This takes place in the liver, which makes 1 mg of vitamin B3 from 60 mg of tryptophan. Vitamin B3 helps release energy from food (see 'The Importance of B Vitamins'). According to the World Health Organisation, adults need 1.3-1.7 mg vitamin B3 a day, and it is found in meat, wholegrains, legumes and peanuts.

Vitamin C

Vitamin C acts as an antioxidant, helps keep cells healthy, and helps people absorb iron from food (see ‘Getting the Right Amount of Vitamin C’).

Most animals can make their own vitamin C, except apes (which includes humans), monkeys, tarsiers, bats, guinea pigs, some birds and some fish. According to the World Health Organisation, adults need 45 mg of vitamin C daily, and they must get this from food every day, as vitamin C is a water-soluble vitamin, so is not stored in the body. Eating five portions of a variety of fruit and vegetables a day should supply the required amount of vitamin C.

The vitamin requirements for people change as they get older, and the requirements generally increase from birth to old age.

Water-Soluble Vitamins

The human body does not store water-soluble vitamins, so these are needed in the diet every day.

Vitamin B1

Vitamin B1, also known as thiamine or thiamine, keeps nerves and muscles healthy, and helps release energy from food. Good sources of vitamin B1 include pork, fruit and vegetables, dairy, milk, eggs and wholegrains.

• Infants (0-12 months) need 0.2-0.3 mg/day
• Children (1-9 years) need 0.5-0.9 mg/day
• Adolescents (10-18 years) need 1.1-1.2 mg/day
• Adults (19-65 years) need 1.1-1.2 mg/day
• Elderly people (65+ years) need 1.1-1.2 mg/day

Vitamin B2

Vitamin B2, also known as riboflavin, keeps skin, eyes, the nervous system and mucous membranes healthy, and helps produce steroids and red blood cells. Good sources of riboflavin include dairy, eggs, rice and mushrooms.

• Infants - 0.3-0.4 mg/day
• Children - 0.5-0.9 mg/day
• Adolescents - 1.0-1.3 mg/day
• Adults - 1.1-1.3 mg/day
• Elderly people - 1.1-1.3 mg/day

Vitamin B3

Vitamin B3, also known as niacin or nicotinamide, keeps the nervous and digestive system healthy and releases energy from food. Good sources include meat, offal, fish, dairy, eggs, wholegrains, peanuts and legumes.

• Infants - 2-4 mg/day
• Children - 6-12 mg/day
• Adolescents - 16 mg/day
• Adults - 14-16 mg/day
• Elderly people - 14-16 mg/day

Vitamin B5

Vitamin B5, also known as pantothenic acid, helps release energy from food. Good sources include meat, vegetables, wholegrains and eggs.

• Infants - 1.7-1.8 mg/day
• Children - 2.0-4.0 mg/day
• Adolescents - 5.0 mg/day
• Adults - 5.0 mg/day
• Elderly people - 5.0 mg/day

Vitamin B6

Vitamin B6, also known as pyridoxine, helps from haemoglobin in blood and releases energy from food. Good sources include meat, fish, wholegrains, eggs, vegetables, soya beans, peanuts and dairy.

• Infants - 0.1-0.3 mg/day
• Children - 0.5-1.0 mg/day
• Adolescents - 1.2-1.3 mg/day
• Adults - 1.3-1.7 mg/day
• Elderly people - 1.5-1.7 mg/day

Vitamin B7

Vitamin B7, also known as biotin, helps release energy from food. Good sources include offal, eggs, fruit and vegetables.

• Infants - 5-6 mcg/day
• Children - 8-20 mcg/day
• Adolescents - 25 mcg/day
• Adults - 30 mcg/day
• Elderly people - 30 mcg/day

Vitamin B9

Vitamin B9, also known as folic acid, helps form blood, and prevents spina bifida in unborn babies. Good sources include vegetables, wholegrains and legumes.

• Infants - 80 mcg/day
• Children - 150-300 mcg/day
• Adolescents - 400 mcg/day
• Adults - 400 mcg/day
• Elderly people - 400 mcg/day

Vitamin B12

Vitamin B12, also known as cyanocobalamin, helps make blood, keeps the nervous system healthy, and releases energy from food. Good sources include meat, seaweed, dairy, fish and eggs.

• Infants - 0.4-0.7 mcg/day
• Children - 0.9-1.8 mcg/day
• Adolescents - 2.4 mcg/day
• Adults - 2.4 mcg/day
• Elderly people - 2.4 mcg/day

Vitamin C

Vitamin C, also known as ascorbic acid, keeps cells healthy and helps the absorption of iron. Good sources include fruit and vegetables.

• Infants - 25-30 mg/day
• Children - 30-35 mg/day
• Adolescents - 40 mg/day
• Adults - 45 mg/day
• Elderly people - 45 mg/day

Fat-Soluble Vitamins

The human body stores fat-soluble vitamins, so while these are needed regularly, they are not needed in the diet every day.

Vitamin A

Vitamin A, also known as retinol, carotene or tretinoin, helps vision, and keeps skin and the immune system healthy. Good sources include dairy, eggs, oily fish and liver.

• Infants - 375-400 mcg/day
• Children - 400-500 mcg/day
• Adolescents - 600 mcg/day
• Adults - 500-600 mcg/day
• Elderly people - 600 mcg/day

Vitamin D

Vitamin D, including vitamin D2 (also known as ergosterol or ergocalciferol); vitamin D3 (also known as cholecalciferol or calcitriol); vitamin D4 (also known as dihydroergocalciferol); and vitamin D5, helps keep bones and teeth healthy by regulating calcium. Good sources include oily fish, eggs and liver, and sunlight.

• Infants - 5 mcg/day
• Children - 5 mcg/day
• Adolescents - 5 mcg/day
• Adults - 5 mcg/day
• Elderly people - 15 mcg/day

Vitamin E

Vitamin E, also known as tocopherol, protects cell membranes. Good sources include plant oils, nuts and seeds.

• Infants - 2.7 mg/day
• Children - 5.0-7.0 mg/day
• Adolescents - 7.5-10.0 mg/day
• Adults - 7.5-10.0 mg/day
• Elderly people - 7.5-10.0 mg/day

Vitamin K

Vitamin K helps blood clotting. Good sources include the gut bacteria, as well as green leafy vegetables, vegetable oils and wholegrains. Infants are given an injection of vitamin K at birth.

• Infants - 5-10 mcg/day
• Children - 15-25 mcg/day
• Adolescents - 35-55 mcg/day
• Adults - 55-65 mcg/day
• Elderly people - 55-65 mcg/day

The figures for daily requirements in this article are from the World Health Organisation report ‘Vitamin and mineral requirements in human nutrition (Second edition), published in 2004.

 Source: www.explorevitamins.co.uk