Since time out of mind, salt has been part of everyday life, prized for its culinary, medicinal and industrial uses. Way back in Roman days, soldiers' wages included a ration of salt or salarium (from the Latin for salt, sal), which survives in the word "salary" and in the expression "to be worth his salt".

Many others testify to salt's place in our culture. For example, "salt of the earth" - describing someone worthy of great esteem - dates from Biblical times, whereas "to sit above/below the salt" recalls a more recent age when salt, savagely taxed, became a luxury commodity. Persons of rank sat near their host - above the ostentatiously-positioned salt cellar - and were allowed some of its contents; less favoured guests sat "below the salt" and were denied its use.

Salt is also the focus of numerous superstitions - a reminder of its former status as a sacred substance: the ancient Chinese had a salt god; nearer home, druids used salt in their sacrifices at Stonehenge. It is hardly surprising, then, that a New Year first-footer's gifts include salt; likewise, spilling salt brings bad luck, redeemed by throwing it over the left shoulder.

Today, however, salt comes with a health warning. The trouble is, we are eating too much salt and it is now widely accepted that a high salt intake can contribute to a number of health problems.

Blood pressure danger

High blood pressure heads the list. Excessive salt consumption raises blood pressure, which in turn increases the risk of stroke and heart attack - the two most common causes of death and disability in the UK. There is even some evidence to suggest a direct link between salt and stroke - independent of blood pressure.

Another condition affected by a high salt diet is osteoporosis. This is because salt intensifies calcium loss, leaving bones thinner, weaker and more vulnerable to fracture. Oedema, too, is associated with a high salt intake. The more salt is consumed, the more fluid is retained in the body, provoking symptoms such as swollen ankles, bloating and over-tight rings on swollen fingers.

Increasingly, evidence also links excessive salt consumption with kidney disease, dementia, Menières disease and stomach cancer. And, in an aggravating role, salt may impact on asthma and migraine.

In all these health conditions, too much salt can be a significant factor. But how much is too much? What constitutes a 'high' salt intake? The UK recommended maximum for adults is 6g of salt per day - one teaspoonful; yet our average daily intake is 9.5g. One of the most alarming aspects of salt consumption is that often people do not realise just how much salt they are having. They equate eating salt with adding it to food - while cooking or at the table - and forget that around 80 per cent of salt intake comes from processed foods: items as basic as bread, baked beans, sausages, soups, pies, pizzas... even breakfast cereals. Not forgetting takeaways and ready meals.

Last year, a survey of high street sandwiches revealed that 22 per cent contained 3g or more of salt - half the daily maximum. A similar survey of canned/carton soups found one, since withdrawn, which had 6.25g of salt in a standard serving; many others contained as much as 2-3g of salt per serving.

The issue of 'hidden' salt - and the ignorance surrounding it - was highlighted by a study carried out among patients attending a specialist blood pressure unit. All the patients maintained they had either cut c down on salt or cut it out completely. Analysis of their urine told another story. Only 13 per cent registered a salt intake of 6g or under; the average was 9.3g, and for one patient - who claimed to have given up salt altogether - it was almost 24g.

Campaigns to cut down

Recognising the relationship between high salt consumption and ill-health, the Food Standards Agency as well as the Department of Health are running salt campaigns aimed both at food manufacturers and the public.

Manufacturers have been challenged to reduce the amount of salt in their food products and, over the past year, this process has gathered momentum. The Co-op, for example, is working towards a minimum salt reduction of 20 per cent in own brand foods. For its part, ASDA - committed to taking out at least 10 per cent of salt - has already reduced salt in its cereals by up to 46 per cent. Birds Eye has achieved a 19 per cent reduction across its range while Tesco is taking out 50 million teaspoons of salt - 282 tonnes - from key products. Although these measures sound promising, remember that the value of any reduction depends on the original level: consumers should still scrutinise nutrition labels.

Labelling is also a concern. At present, some nutrition labels give sodium content only, rather than sodium plus salt equivalent. From a health point of view, sodium is the culprit. It is contained in salt - sodium chloride - and in other ingredients such as monosodium glutamate, sodium bicarbonate and baking powder. Putting sodium on the label does give a more accurate picture, but many people find this meaningless. So, as almost all the sodium in food comes from salt, there is a move to indicate salt equivalent alongside sodium content. Until this happens, there is no need to plead ignorance. Either do a simple sum: sodium x 2.5 = salt; or learn the recommended maximum for sodium: 2.4g per day.

In addition to providing detailed nutrition data, manufacturers are being urged to show salt levels on the front of packs. Examples of this include the Co-op roundel, introduced in 1998, which displays calories, fat and salt values, and Sainsbury's 2005 initiative - the colour-coded "wheel of health". This type of at-a-glance information can be crucial: on average, shoppers take just four seconds deciding which product to buy.