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An A-Z guide of vitamins and minerals

By Irish Pharmacist - 05th Mar 2024

Eamonn Brady examines the various vitamins and minerals, where they can be found, and how they can help to protect you against an array of illnesses

Vitamin A and Beta Carotene

Vitamin A helps you see in the dark. It helps your eyes adjust to darkness after being exposed to bright light, like the headlights of an oncoming car at night. You can also thank vitamin A for healthy skin, strong bones, and a sound immune system. The vitamin itself shows up primarily in organ meats, but many fruits and vegetables contain beta-carotene and other carotenoids that are converted to vitamin A in the intestine. Eating foods rich in these substances may protect you against heart disease and certain forms of cancer.

What foods are the best sources of vitamin A?

Orange, red, and dark green vegetables, and fruits, are particularly rich in beta-carotene and the 50 other carotenoids that the body converts to vitamin A. Just one red pepper or half a cup of spinach contains enough to meet your daily requirement for A. But the more carotenoids you get, the better, so don’t be afraid to load up on foods with vitamin A.

Liver is by far the richest source of vitamin A – so rich that you probably shouldn’t eat it more than once a week. Fish and egg yolks are also packed with it, and some brands of milk are fortified with A, to help your bones absorb calcium.

Should I take a supplement?

No. You’re not likely to be deficient in the vitamin, and vitamin A supplements can easily give you a toxic dose, and while beta-carotene supplements are probably not harmful, they won’t give you all the health benefits of carotenoid-rich foods. Researchers in Finland found that smokers who took vitamin A supplements were slightly more likely to develop lung cancer.

Can I get too much vitamin A?

Yes. As little as 10,000 mcg of vitamin A per day can cause birth defects in pregnant women and, over time, headaches, hair loss, and liver damage. But unless you’re eating a lot of liver, it’s hard to get that much from your diet. You can’t overdose on carotenoids, and your body will only convert what it needs to vitamin A.

B vitamins

The B vitamins are often referred to as the ‘energy’ vitamins, mainly because they are involved in energy release in the body. There are in fact eight different B vitamins, each with a different role in the body. The eight B vitamins are Vitamin B1, B2, B3, B5, B6, B7, B9 and B12. Getting enough B vitamins helps keep energy levels up, increases mental alertness, helps memory, boosts the immune system, and perhaps even helps to fight depression. Many elderly people, vegetarians, or people who are on strict diets, don’t get enough of these important vitamins.

People living with stress, eat out often, don’t have a good balanced diet with plenty of fruit and veg, or abuse alcohol, can also be deficient.

Types of B vitamins

Vitamin B1 is also called thiamine. It helps to regulate mental functions and nerve growth and can help with memory. It also helps convert food to energy. Thiamine can be found in whole grains, beans, oranges, peas, peanut butter, pork, liver, and fish. A deficiency of vitamin B1 is common among people who abuse alcohol and alcoholics therefore need more thiamine. Alcohol reduces the absorption of thiamine in the body, so vitamin B1 supplements are often needed by alcoholics. Heavy smokers or people who consume too many carbohydrates have a greater need for vitamin B1. Stress-related conditions will also deplete vitamin B reserves within the body including vitamin B1. The recommended daily allowance of vitamin B1 is 1.4mg.

Vitamin B2 is also called riboflavin. It releases energy from foods, makes many of the body’s hormones, and helps growth and development. It can be found in dairy products, green leafy vegetables, avocados, meat, beans, and nuts. A shortage of this vitamin may cause cracks and sores at the corners of the mouth, eye disorders, inflammation of the mouth and tongue, and skin lesions. The recommended daily allowance of vitamin B 2 is 1.2mg.

Vitamin B3 is also called niacin and is used for more than 50 body processes including releasing energy from food, making hormones, removing toxins, and helping to keep cholesterol within the normal range. Niacin can be found in dairy products, meat, chicken, fish, beans, peas, nuts, and peanut butter. Vitamin B3 deficiency is rare in Ireland, with alcoholism being the most common cause. The recommended daily allowance of vitamin B3 is 18mg.

Vitamin B5 is also called pantothenic acid. It releases energy from food. It works with other B vitamins to help break down proteins, fats, and carbohydrates, from food to give the body energy. It is also needed to make vitamin D and red blood cells. It can be found in liver, fish, chicken, beans, and whole grains. Deficiency of vitamin B5 can cause fatigue, headaches, nausea, tingling in the hands, depression, personality changes, and cardiac instability have been reported. The recommended daily allowance of vitamin B5 is 6mg.

Vitamin B6 is also known as pyridoxine. It can help prevent heart disease and reduce depression. We get pyridoxine by eating fish, chicken, potatoes, bananas, peas, beans, and avocados. Signs of vitamin B6 deficiency include dermatitis (skin inflammation), glossitis (a sore tongue), depression, confusion, and convulsions. The recommended daily allowance of vitamin B6 is 2mg. Deficiency in Ireland is rare, and only occurs in people with extremely poor diets.

Vitamin B12 helps in the formation of red blood cells and in the maintenance of the central nervous system

Vitamin B7 is also called biotin. It helps to break down the proteins, carbohydrates, and fats into energy. We get biotin by eating liver, salmon, clams, eggs, milk, peanut butter, and bananas. Long-term antibiotic use can interfere with biotin production in the intestine and increase the risk of deficiency symptoms, such as dermatitis, depression, hair loss, anaemia, and nausea. Long-term use of anti-epilepsy medications may also lead to biotin deficiency. The recommended daily allowance of vitamin B7 is 300mcg.

Vitamin B9 is more commonly called folic acid and helps cells grow and divide properly, prevents birth defects, and prevents heart disease. We get folic acid by eating dark green leafy veggies, avocados, beets, orange juice, beans, and liver. Women planning to conceive should take folic acid 400mcg daily prior to conception and for the first 12 weeks of pregnancy. This prevents spina bifida in the newborn child. Folic acid 400mcg is available over the counter in pharmacies for women trying to conceive and for the first 12 weeks of pregnancy. It is also available on the medical card (GMS). The normal recommended daily allowance of folic acid for all other adults is 100mcg. Most people assume folic acid is only needed during pregnancy. However folic acid is important at all ages to properly form red blood cells and for our bodies to metabolise protein for energy.

Vitamin B12 is also called cobalamin. It breaks down proteins, carbohydrates, and fats to give energy. Vitamin B12, like the other B vitamins, is important for metabolismmetabolism. It helps in the formation of red blood cells and in the maintenance of the central nervous system. It also helps prevent heart disease, and combats depression. You can get cobalamin by eating eggs, milk, yogurt, chicken, fish, and meat. Because vitamin B12 comes primarily from animal products, people who follow a strict vegetarian or vegan diet and do not consume eggs or dairy products may require vitamin B12 supplements. Those who had surgery on specific parts of the small intestine or stomach are also prone to a deficiency if they do not take B12 supplements. Low levels of B12 can cause anaemia, numbness or tingling in the arms and legs, weakness, and loss of balance. The recommended daily allowance of vitamin B12 is 6mcg. For people who are deficient in vitamin B12, their GP may decide to prescribe vitamin B12 injections. If this is the case, a 1000mcg cobalamin injection is generally given once monthly via an intramuscular injection.

Vitamin E

Vitamin E works together with other antioxidants, such as vitamin C and selenium, to help prevent chronic illnesses such as diabetes and heart disease.

Vitamin E captured the attention of cardiologists in 1993, when a Harvard University study showed that men who took vitamin E had a 35 per cent lower risk of heart disease than those who didn’t take the supplement. These results bolstered the theory that vitamin E helps keep heart problems at bay by preventing so-called bad cholesterol (LDL) from clogging up your arteries.

Vitamin E is most found in vegetable oils, nuts, fatty fish such as tuna and salmon, dark, leafy vegetables, and whole grains. Frying or cooking with a lot of oil could cause a loss of vitamin E. If you tend to skimp on vegetables, nuts, and whole grains, you may benefit from taking a vitamin E supplement.

Vitamin D

Your body also needs vitamin D to absorb calcium properly. Vitamin D is found in certain foods, including cod liver oil, oily fish such as sardines and herrings, margarine, and egg yolks. It’s also made by your skin when in the sunlight. The National Osteoporosis Society recommends about 20 minutes of sun exposure to the face and arms every day during the summer to provide you with enough vitamin D for the year. However, to reduce your risk of getting skin cancer, you should cover your skin between 11am and 3pm, and don’t allow your skin to burn. Between 40 to 80 per cent of people over 65 have vitamin D deficiency in Ireland. Vitamin D deficiency also causes a mild muscle weakness and hence increases the risk of falls and consequential fractures. Therefore, vitamin D supplementation is especially important in this age group. Supplements are commonly prescribed for patients over 65, especially as new evidence emerged since 2020 that it can help prevent protection from infections like Covid-19. In recent years, they are available in once monthly oral forms to increase convenience and compliance.

New research

Between 40 to 80 per cent of Irish people over 65 have a vitamin D deficiency. Research has found that a daily supplement of 700 to 1000IU of vitamin D reduces the risk of fractures from falls among older people by 19 per cent. The British Medical Journal shows that a dose of less than 700IU per day has no effect in reducing fractures. Research is also showing that vitamin D plays an important role in helping the immune system. It may also help to prevent illnesses like diabetes, heart disease, rheumatoid arthritis, multiple sclerosis as well as some forms of cancer.

Drug interactions

Some blood pressures called diuretics (eg thiazides) can reduce the urinary excretion of vitamin D, hence increasing the risk of too much vitamin D. Some epilepsy medication such as phenytoin can reduce vitamin D levels.

Vitamin D in infants and children

Guidelines regarding vitamin D were released in 2010 by the Food and Safety Authority of Ireland and the Department of Health. It is recommended that all infants, from birth to 12 months, whether breastfed or formula fed, be given a daily supplement of 5 µg (200 IU) vitamin D. This should be provided by a supplement containing vitamin D exclusively. These guidelines were released because children (and adults) in Ireland have been found to have low levels of vitamin D. There has been an increase in the number of cases of rickets in Ireland in recent years.

Babies need vitamin D supplements for the following reasons:

  • Babies’ skin is very sensitive to the sun and should not be exposed to direct sunlight;
  • Babies’ food (breast milk, formula milk or solid foods) may not have enough vitamin D;
  • Between 0-12 months, babies grow very quickly and have a greater need for vitamin D to form strong bones.

Babies with African, Afro-Caribbean, Middle-Eastern or Indian ethnic backgrounds are at even higher risk of having low levels of vitamin D. Their stores of vitamin D may be particularly low when born as their mothers’ skin may not be as efficient at making vitamin D from the low levels of sunlight experienced in Ireland.

What type of vitamin D supplement should be given to a baby?

Vitamin D3 (cholecalciferol) is the preferred form of vitamin D for infants. Liquid form is best. Products that contain other vitamins as well as vitamin D (such as multivitamin products) should not be used. Very high amounts of vitamin D are harmful. The recommended 5mcg vitamin D a day is very safe for babies. Harmful effects only begin at levels that are five times higher than this recommended dose.


Eating a diet rich in calcium is important for maintaining healthy bones. Dairy products and green leafed vegetables are good sources of calcium. Postmenopausal women with osteoporosis should aim to take 1,000mg of calcium every day, either in their diet or as a supplement. This can be obtained from 600ml of milk with either 50g of hard cheese (eg Cheddar or Edam), one pot of yogurt, or 50g of sardines. Care must be taken as many dairy products are high in fat; however, the low-fat versions have the exact same calcium levels as full fat versions. You should try not to drink fizzy drinks or have too much caffeine, salt, or animal protein such as beef, as these can affect the balance of calcium in your body.

Eating plenty of fruit and vegetables can help to cancel out the effects of too much protein in your diet. Smoking can have a harmful effect on your bone strength and can also cause an early menopause. If you smoke, you should try to give up. You should also be careful not to drink too much alcohol.

Hair, skin and nails

Nutritional deficiencies can contribute to increased hair loss by weakening hair shafts that cause breakage to the hair and slow regrowth. Hair problems that are caused by nutritional deficiencies can be corrected by a good diet. The main nutrients involved in hair health include vitamin A, certain B vitamins, the vitamin biotin, vitamin C, copper, iron, zinc, protein, and water. Of all nutrients, biotin has the biggest impact on hair growth. It is found in food sources such as eggs and liver, however if somebody has thinning or damaged hair, a biotin supplement is a good choice.

Lutein for eyes

Age Related Macular Degeneration (AMD) is thought to affect one in 10 people over the age of 55. More than 60,000 Irish people suffer from this condition in Ireland. Lutein, Zeaxanthin, bilberry, and grapeseed are recommended to reduce the risk or slow the progression of AMD. They are available in over-the-counter supplements designed to reduce the risk and slow down the progression of AMD in at-risk patients.

Overload of fat-soluble vitamins

There are two general classes of vitamins, water soluble and fat soluble. Water soluble vitamins include the B vitamins and vitamin C. They dissolve in water and are not stored by the body. Excess amounts are excreted in urine which means that you cannot overdose on them. They must be replaced every day in our diet to provide a continuous supply. Fat soluble vitamins include vitamin A, D, E and K. Fat-soluble vitamins are found mainly in fatty foods such as animal fats including butter and lard, vegetable oils, dairy foods, liver, and oily fish. Unlike water soluble vitamins, they are not excreted when our body takes in too much, instead they can build up in fat tissues and various organs in the body such as the liver. Therefore, overdose is possible. Overdose of fat-soluble vitamins is very unlikely with food alone; however, some multivitamins have high levels of fat-soluble vitamins. Therefore, if taking several vitamin supplements, always check you are not doubling up on fat soluble vitamins. A common example of inadvertent overdose of vitamin A and D is taking cod liver oil with a multivitamin. This is because cod liver oil has high levels of vitamin A and D. Instead, of taking cod liver oil with a multivitamin, you can simply take a fish oil supplement which has the benefits of omega 3 but has no vitamin A or D. Vitamin A is needed for the wellbeing of our eyes, bones, and reproductive organs. Signs of vitamin A toxicity include dry, itchy skin, headache, nausea, and loss of appetite. Overdose is dangerous in pregnant women as it can damage the foetus. Vitamin D helps the hardening of bones and teeth and increases the absorption of calcium. Overdose can cause nausea, weight loss and irritability. It can also damage the unborn foetus. There is however little evidence of toxicity with too much vitamin E and K.

Vitamin D helps to harden bones and teeth and increases the absorption of calcium. Overdose can cause nausea, weight loss and irritability


Vitamin C helps the absorption of iron so, if you must take an iron supplement for anaemia, it is a good idea to take a vitamin C supplement or a fruit high in vitamin C at the same time. Ferrograd C® is an iron supplement that contains a slow releasing iron and vitamin C. The fact it is slow releasing leads to lower incidence of side effects such as nausea and constipation. Antacids such as Rennies® and Gaviscon® can reduce the absorption of iron by up to 30-40 per cent. Tea and coffee also cut the absorption of iron, as their tannins bind to iron, thus reducing its absorption. Therefore, iron supplements should be taken at a different time to antacids and tea/coffee. Iron can reduce the absorption of some prescription medication. For example, it reduces the absorption of bisphosphonates used for osteoporosis, and some commonly used antibiotics including fluoroquinolones (eg Ciprofloxacin) and tetracyclines (eg Minocycline, Doxycycline). In fact, iron can reduce the absorption of tetracycline antibiotics by 50 to 90 per cent. Tetracyclines are mainly used for the treatment of chest infections (especially bronchitis), acne and malaria prevention. Iron should be taken at least three hours apart from these medicines.


It is contained in foods such as chicken, meat, and fish. It is a significant component of more than 300 enzymes and plays a vital role in carbohydrate metabolism, protein synthesis, wound healing, the immune system, digestion, sugar level control, and the senses of taste and smell. 

Disclaimer: Brands mentioned in this article are meant as examples only and not meant as preference to other brands.

Author: Eamonn Brady MPSI (Pharmacist). Whelehans Pharmacies, 38 Pearse St and Clonmore, Mullingar. Tel 04493 34591 (Pearse St) or 04493 10266 (Clonmore). Eamonn specialises in the supply of medicines and training needs of nursing homes throughout Ireland. Email

References on request






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