To supplement or not to supplement - that is the question facing health-conscious consumers. Confronted with rows of glistening products in the high street and bombarded with persuasive messages from advertising hoardings, how are they to know whether they really need those extra vitamins or not?

Go to the Food Standards Authority (FSA) website and you will be told that most people can get all the nutrients they require from their diet. Visit a chemist or health food store and you immediately enter the arena of vested interest: how can you be sure that your health - rather than company profits - is of paramount concern to the person behind the counter?

About one person in three takes a food supplement, according to a recent FSA survey, and nearly half said that they had never received advice or looked for information about the supplements they should be taking. The same number did not know enough about safe levels, and almost one in ten believed that it was safe to take as many vitamin and mineral tablets as they liked. “It is virtually impossible to overdose on nutrients in food but easy to overdose on supplements,” says Catherine Collins, the chief dietitian at St George's Hospital in South London. “People think more is better, but you would not take more paracetamol than the stated dose.”

So how do we make our way through this minefield of echinacea and glucosamine and avoid hurting our bank balance, and potentially our health, by taking needless supplements?

According to Collins, it's always better to obtain your nutritional needs from your diet. However, if you feel that your diet is lacking, it may be worth popping some vitamin pills. As to what brand to buy, Collins recommends sticking with the cheapest.

MULTIVITAMINS

Good for: General health

Cost: £3.99 for 60 tablets, hollandandbarrett.com

A good all-rounder. Children may benefit from one a day, particularly if they are fussy eaters. At the other end of the spectrum, a low-dose vitamin and mineral supplement may help to reduce the incidence of chest infections in elderly people.

For the rest of the population, multivitamins may well have a beneficial effect on health, but they will never compensate for a lack of exercise, or eating chips three times a week; lifestyle is key to staying in good health.

VITAMIN D

Good for Strong bones, and a healthy immune system.

Cost £3.55 for 90 tablets (with calcium), boots.com

A recent report found that most people in the UK are deficient in vitamin D. Production is stimulated by sunlight, but in our cold, gloomy climate we don't get outdoors enough to keep our body topped up with this essential vitamin. Levels should peak around this time of year; the vitamin D produced in the summer is stored in our body fat. Sadly, as all those people who holidayed in the UK this year will appreciate, we barely had enough sunshine to warrant wearing shorts, let alone stimulate vitamin D production. Consequently, blood tests taken around this time of year reveal that our levels are low.

Vitamin D deficiency has been associated with a higher incidence of auto-immune disease, including rheumatoid arthritis, multiple sclerosis and type 1 diabetes. Our immune system may also be affected, as can bone density. Oily fish, liver or paté are good sources, but if they make your stomach turn, consider a supplement.

FISH OIL

Good for: Heart health, joints

Cost: £9.50 for 150 capsules, boots.com

Research indicates that omega-3 fats, found in fish oil supplements, can help to stabilise abnormal heart rhythms, reducing the risk of heart attacks.

However, they are effective only when taken as part of a healthy diet. Cut back on saturated fats, found in cakes and biscuits, and polyunsaturated omega-6 fats, found in corn and vegetable oil, and increase your intake of monounsaturates, such as olive oil.

If you are taking medication for a heart condition or high blood pressure, check with your GP that they won't interact with omega-3 supplements. Omega-3s also have anti-inflammatory effects, and may help conditions such as arthritis. But forget about fish oils boosting your brain cells. There is still a lack of conclusive evidence to suggest that omega-3 products will improve intelligence or cognitive function. Back to the crosswords and Su Doku then.

GLUCOSAMINE

Good for: joints

Cost: £4.99 for 30 tablets, superdrug.com

Evidence of glucosamine's effectiveness is mixed. A clinical trial of 1,500 people with arthritis showed that a higher number of people found it effective compared with a placebo, but this difference was not statistically significant. In other words, taking glucosamine is no better than gulping a sugar pill. However, arthritis trials are notoriously difficult, as the condition is prone to relapse and remission. Consequently, the advice is to give it a whirl, but don't expect miracles.

ECHINACEA

Good for: colds

Cost: £5.99 for 30 tablets, superdrug.com

This helps to boost the immune system, specifically the action of a set of immune cells called natural killer cells. This may help to reduce the severity of a cold.

However, it works only at the onset of cold, so start taking it as soon as you get symptoms. Further, your body becomes tolerant to it after around a week, so remember to stop taking it once the cold has passed.

ST JOHN'S WORT

Good for: Depression

Cost: £8.49 for 100, hollandandbarrett.com There is evidence that this is an effective mild antidepressant. Side-effects include reducing the effectiveness of oral contraceptives, so see your GP before taking it.

ONES TO AVOID

Vitamins C and A

There is little evidence to suggest that vitamin C can ward off colds. In a study published earlier this year, high doses of vitamin A were linked to weak bones, and even premature death. There's no need to panic if you're already taking a vitamin A supplement, but don't waste your money on any more

COMPILED BY KATE WIGHTON

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