Eating a healthy diet, as promoted in our dietary guidelines, is designed to meet our need for all vitamins, with the exception of vitamin D. People with anorexia nervosa, or those with certain severe allergies who don’t eat regular foods, usually need a good multivitamin. Sadly, the available offerings are not well balanced, usually containing many times the recommended dietary intake (RDI) for some vitamins, but often lacking sufficient quantities of others.
Consuming more of some vitamins than you need may simply result in the excess being flushed out in urine. Others can be dangerous, causing adverse reactions or interfering with other essential medications. Unfortunately, the labels don’t list the RDI so it can be hard to know if they are safe. Nor do they list the safe Upper Level – a value included in Australia’s Nutrient Reference Values. Some labels still give the quantity of vitamin A in International Units – an old terminology that was discarded in 1961!
Fat-soluble vitamins
Fat-soluble vitamins (A, D, E and K) are hazardous in excess.
Vitamin A is found in butter, margarine, cheese, full-fat milk and yoghurt, oysters and some fish. However, we don’t actually need to eat this form of vitamin A because the body can easily make all it needs from beta carotene, found in yellow, orange and green vegetables and fruit. If you eat loads of, say, carrots, your skin may turn an orange-yellow colour. This may look odd, but it’s not a health hazard. However, beta carotene in supplements has been found to increase health problems in smokers.
Vitamin A itself (also known as retinol) is hazardous in excess. In Australia, supplements containing Vitamin A must carry a warning that they’re not suitable during pregnancy, as they can lead to birth defects. Anyone with liver disease should also avoid supplements containing vitamin A.
Vitamin D is found in small amounts in fatty fish, eggs and mushrooms that have been exposed to UV light. The best way to get enough is by exposing the skin on the arms for a few minutes each day, a little longer during winter, preferably around midday. The body can store vitamin D and that helps when it may be too cold to pull your sleeves up. Like most nutrients, more is not better. Too much sun on the skin is a major factor in Australians’ high rates of skin cancers.
Vitamin E is found in seeds, nuts, peanut butter, wholegrains, vegetables (sweet potato comes top) and vegetable oils (especially sunflower and safflower). Claims that supplements will help prevent or treat heart disease or cancers are not supported by evidence. Deficiency is rare and large doses can increase the risk of some types of stroke. The upper safe limit is 300 mg/day.
Vitamin K exists in several forms (often called K1, K2 and K3). It is essential for normal blood clotting. Green vegetables are a top source and it’s also found in fermented foods, cheese, yoghurt, soy beans and nuts. One form of vitamin K is made by bacteria in the intestine. Anyone taking long-term antibiotics or warfarin needs to ensure a consistent intake of green vegetables and may be prescribed a supplement.
Water-soluble vitamins
Vitamin B consists of eight different vitamins: B1 thiamin (spellcheckers incorrectly add an ‘e’, which was omitted when its structure was identified); B2 riboflavin; B3 niacin; B6 existing as one or more forms of pyridoxine; B12 cyanocobalamin; folate; pantothenic acid; and biotin. The missing numbers arose when some substances previously assumed to be part of the B complex were found not to be vitamins.
For most of the B vitamins, any excess is flushed out in urine. However, excess vitamin B6 is a problem, increasing the risk of peripheral neuritis with potentially permanent damage to the nerves in fingers and feet. This is not a new problem and I included warnings about it in my books over 35 years ago. However, many supplements often contain massive quantities – 100 mg in some multivitamins and it’s being added to many magnesium supplements. The RDI ranges from 1.3 to 1.7 mg/day. The Therapeutic Goods Authority (TGA) now requires products containing a daily dose of vitamin B6 above 10 mg to include a warning about peripheral neuropathy.
Folate (the name is derived from foliage – as in leafy vegetables) is needed for growth of all body cells. This is especially important during conception and the early weeks of pregnancy and is the reason why the RDI for pregnant women is 1.5 times that for adults. It is possible for a healthy diet to include enough, with vegetables, legumes, nuts, seeds, fruits (especially citrus, bananas and strawberries), avocado and eggs supplying it. Liver, especially chicken liver, is a rich source. In Australia, folic acid, a synthetic form of folate, is now added to bread flour and many breakfast cereals. This has reduced the incidence of neural tube defects in babies. As with most vitamins, more is not better. The Upper Limit is 1000 micrograms of folate equivalents (which equate to 600 micrograms of folic acid).
Vitamin B12, like vitamin A, is not found in plant foods, but comes in meat (especially liver), fish, eggs and dairy products. The vitamin has a complicated path within the body. In the stomach, acid and an enzyme (pepsin) free the B12 from food, and it attaches itself to proteins from swallowed saliva. Stomach cells then release a glycoprotein called intrinsic factor and the stomach contents pass to the small intestine. At the lower end, an enzyme from the pancreas then frees the B12 from intrinsic factor so it can be absorbed. Fortunately several years supply of B12 is stored in the liver. Some bacteria in the large intestine can make small amounts of B12, but those on a vegan diet need a supplement. So do some frail aged people as the complicated absorption path often falters. B12 analogues in comfrey and spirulina aren’t a substitute for the real thing. Fortunately B12 toxicity is low.
Biotin is made by bacteria in the intestine and found in many foods including legumes, oats, nuts, eggs and seafood. Supplements are only needed for anyone who eats lots of raw egg white as the avidin in them binds biotin so it can’t be used.
Pantothenic acid is also found in many foods, including chicken, meat, grains, nuts and mushrooms. Deficiency is rare and you’d need to take thousands of times the RDI for toxicity from supplements.
Vitamin C is easily provided by fruit and vegetables. Australia’s RDI is 45 mg/day for adults, more during pregnancy and breastfeeding. An orange has about 75 mg, a smallish potato or a modest serve of green beans or three cherry tomatoes each have about 30 mg. Many good trials show that taking supplements doesn’t prevent or cure a cold. Taking 500 to 1000 mg of vitamin C is five to 10 times the body’s saturation level and may cause diarrhoea and act as a pro-oxidant, potentially damaging body cells and tissues. Very high doses also increase the risk of kidney stones. When taken as chewable tablets, the high acidity of vitamin C (ascorbic acid) damages dental enamel – a major problem for children.
Take home message
Unless there are good reasons, get your vitamins from food and appropriate levels of sun for vitamin D. If your diet is so poor that it lacks vitamins, it’s also likely to be low in other nutrients and dietary fibre.
Dr Rosemary Stanton OAM
