What are vitamins and why do we need them?

You might know a bit about vitamins, and may even take some every day, but do you really know what they are? We’ve got the answers to your vital vitamin questions

By Madeleine Bailey on January 23, 2019 Reviewed by Dr Sarah Schenker on January 30, 2019

Most of us know that vitamins keep us healthy, and some have special roles to play – vitamin C can help protect against colds, for example. But beyond that, what do vitamins do, and why do we really need them? Get all the essential facts on these essential nutrients, below.

What are vitamins?

Vitamins are compounds that our bodies need to work properly. Because we can’t make most of them, we have to get them from our diets. There are 13 vitamins altogether and they are classed as micronutrients because we only need them in small quantities, usually milligrams (mg) or micrograms (mcg or μg), every day.¹ One exception is vitamin D, which we make through the action of sunlight on our skin. We can also make vitamin B3, known as niacin, from an amino acid called tryptophan – though we still need to get that from food such as nuts, seeds, tofu, cheese, meat, fish, oats, beans, lentils and eggs.²

Why do we need vitamins?

Without them, our bodies wouldn’t be able to perform vital tasks such as converting food into energy, building and maintaining bones, teeth, muscle, skin, blood and hair, and keeping our brain, eyes, nervous and immune systems in good working order.³ Some vitamins work together with other nutrients: vitamin C helps us to absorb iron from plant foods,⁴ while vitamin D helps us absorb calcium.⁵ And the vitamins A, C and E all have an antioxidant effect, which means they help protect our cells from damage by free-radicals.⁶

The different types of vitamins

Vitamins fall into two groups: water-soluble and fat-soluble. The fat-soluble vitamins A, D, E and K can be stored in our liver and fatty tissues. This means we don’t have to consume them every day, but there is a risk that they can build up in the body, which may be harmful.

We can’t store the water-soluble vitamins C or the eight B vitamins: thiamin, riboflavin, niacin, pantothenic acid, biotin, folate and B12,⁷ so we get rid of any excess in our urine.

What are the most important vitamins?

All vitamins are essential, but we need to consume the water-soluble vitamins every day because we pass out any excess. Luckily, they are found in plenty of different foods. Besides oranges, vitamin C can be found in broccoli, strawberries, red and green peppers, Brussels sprouts and even potatoes!⁸ And you can get your Bs from wholegrain foods, fortified cereals, rice, oats, liver, meat, fish, dairy products, eggs, potatoes, broccoli, spinach, soya beans and pulses.⁹ Many of us have low stores of vitamin D,  important for bones, muscle and immunity. In the UK we can only make vitamin D through exposure to sunlight from April to October; in the winter, the angle of the sun’s UV rays is lower, which means vitamin D cannot be created. People at risk of low vitamin D levels are those who don’t go outside much, people with dark skin or those who cover their skin.¹⁰ Food sources of vitamin D include oily fish, eggs, fortified cereals, meat and fat spreads.¹¹

What’s the best way to consume vitamins?

A healthy balanced diet should provide all the vitamins you need, but supplements can help plug any nutritional gaps or restore low levels after illness or periods of poor eating. The government also recommends that everyone takes 10mcg of vitamin D per day, especially in winter.¹² Women are strongly advised to take 400mcg folic acid per day when trying to conceive, until the 12th week of pregnancy. This is important for preventing birth defects in the baby, such as spina bifida.¹³ There’s also some concern that our food isn’t as nutritious as it was due to modern farming and food production processes,¹⁴ which is why some people take a multivitamin as an insurance policy.

What happens if we don’t get enough vitamins?

We can develop deficiencies. For example, vegans and some vegetarians are at risk of a vitamin B12 deficiency because it’s mainly found in animal foods.¹⁵ A B12 deficiency can lead to fatigue, depression and serious nervous system problems.¹⁶ People with conditions that may affect with nutrient absorption, such as coeliac disease or Crohn’s disease, may be at risk of several deficiencies, as can those taking certain medications and the elderly;¹⁷ older people may not be able to absorb nutrients properly due to declining levels of stomach acid. However, it’s more common for people in the UK to have low intakes of certain nutrients rather than a deficiency. Smokers may have low levels of vitamin C,¹⁸  heavy drinkers of B vitamins¹⁹ and overweight and obese people have been found to have low levels of  vitamins C, D, B12 and folate.²⁰

Low levels of key vitamins can lead to vague symptoms such as fatigue, aches and pains, low immunity, low mood, and skin, hair and nail problems.

What happens if we take too many vitamins?

Too much vitamin A from food or supplements can lead to liver and bone damage, and cause birth defects.²¹ However, you’d need to consume excess amounts every day over several years for vitamin A levels to become harmful. And although we flush out excess amounts of water-soluble vitamins in our urine, high levels of vitamin C can cause diarrhoea, while too much niacin over time can lead to liver damage.²²

If you’re taking several supplements, make sure you’re not doubling up on vitamins – taking a multivitamin as well as cod liver oil, which is rich in vitamin A, for example.

Shop Vitamins Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.

Sources

1. British Nutrition Foundation. Vitamins 2. Daisy Whitbread. My Food Data. Top 10 foods highest in tryptophan 3. Harvard Health Publishing. Listing of vitamins 4. Verena Tan. Healthline. How to increase the absorption of iron from foods 5. Harvard Health Publishing. Two keys to strong bones: Calcium and vitamin D 6. BBC iWonder. Antioxidants: The magic bullet? 7. Christian Nordquist. Medical News Today. Vitamins: What are they and what do they do? 8. NHS. Vitamin C 9. NHS. B vitamin and folic acid 10. gov.uk. PHE publishes new advice on vitamin D

11. As Source 1
12. As Source 10
13. As Source 9

14. Scientific American. Dirt poor: Have fruits and vegetables become less nutritious? 15. The Vegan Society. Vitamin B12 16. Mayo Clinic. Vitamin deficiency anaemia 17. Karen Appold. Today’s Geriatric Medicine. Dangers of vitamin B12 deficiency 18. Netdoctor. Smoking and nutrition 19. Leiber CS. National Institute on Alcohol Abuse and Alcoholism. Relationships Between Nutrition, Alcohol Use, and Liver Disease 20. Ruxton CHS. Nutritional implications of obesity and dieting