There is a flood of advice from medical, nutritional and public health authorities about the changes we should be making to our lifestyle in order to reduce, amongst other health problems, our risk of high blood pressure. High on the list of their recommendations is the one where we are advised to reduce the amount of salt we eat.

It is generally recommended that our daily intake of sodium should be limited to no more than 2400 milligrams per day - that is equivalent to about one teaspoon full ? and that is across our whole daily food intake.

However, like many dietary recommendations aimed at improving our health, it now appears that there could be, or in fact is, a potential downside to this practice of reducing our sodium intake ? if we reduce it too much.

Recent research indicates that lowering our intake of sodium can have the very serious consequence of lowering our iodine consumption.

Iodine is an essential component in the production of the hormones manufactured by our thyroid glands. In children, a properly functioning thyroid is critical to both their physical and mental development. In adults, the hormones from the thyroid gland regulate our metabolism ? that process which regulates our basic cell functions, one of the most important of which is deriving energy from the foods we eat.

For many generations, thyroid disease ? the under functioning of the hormone production by the thyroid glands resulting from lack of adequate iodine levels - was a major health problem not only in the US but in other countries too. This relatively widespread health problem, it was eventually discovered, was mainly due to low levels of natural iodine in the many local water supplies. In areas where iodine did not occur naturally in soils of water catchment areas, or only occurred at very low levels, whole communities were suffering degrees of thyroid disease.

The Recommended Dietary Allowance [RDA] of iodine for adults is 150 micrograms a day. To ensure whole populations throughout the world were receiving their RDA of iodine many countries introduced very successful public health interventions by requiring iodine to be added to table salt. This does not affect the taste of the salt, has no deleterious side effects and adds only marginally to the cost of salt production. However, in many countries, including the US, only table salt has added iodine. The salt used in commercial food processing ? and this is where we get most of our daily salt intake from - usually does not contain iodine.

By reducing the amount of table salt we use in cooking our own food, and also reducing our use of the salt shaker at the table, we are reducing our iodine intake. These lower levels of iodine intake, according to research published by Stephen Cann from the University of British Columbia in 2006, are resulting in significant increases in the levels of iodine deficiency related thyroid problems across whole populations.

He claims that health surveys conducted in the US during the 1970s revealed that 1 in 40 Americans were suffering from moderate to severe levels of iodine deficiency. But, alarmingly, similar surveys during the 1990s reveal that this figure has now increased to 1 in every 9 of the US population.

This unexpected outcome is creating a dilemma for health authorities and more education programs will be necessary to advise people about the need to monitor salt intake to ensure that adequate levels of iodine intake are maintained.