A study of common high street products found that some failed to declare all their ingredients, particularly sweeteners and additives.

Some contained unexpected ingredients such as lead and arsenic and high levels of sodium.

Others failed to make clear that they contained animal and insect products such as gelatine and cochineal.

The survey was conducted by the Food Commission and its results were published in the Food Magazine.

Hidden information

Dr Tim Lobstein, co-director of the commission, said: "We found some companies hide the information in small print while others do not declare their full ingredient list at all, and some make you open the packet to find out what you've been sold."

He added: "We found vitamin pills containing colouring agents that have been banned from virtually all foods."

An example of this, he said, was Redoxen slow-release vitamin C pills. They contained E104 and E127 (erythrosine).

The survey found evidence of "poor and inconsistent labelling". It said many companies "give only the legal minimum indication" of what the active ingredient in the product is.

It also found sweeteners in "a wide range of products". Not all companies specified which sweetener was used.

In the case of a vitamin supplement designed for children, Sanatogen Children's Gold, it found three sweeteners - sorbitol, xylitol and mannitol.

Sorbitol and mannitol are sugars derived from alcohol. They are slowly absorbed from the intestines and may produce a laxative or gaseous effect.

But xylitol has been found to have unusual properties, such as reducing the incidence of earache in children and improving oral hygiene.

Animal products

"It is not always obvious when food supplements are suitable for vegetarians," the survey said.

Most commonly used was gelatine, which comes from the skin, bones and connective tissue of cattle and pigs.

The survey said there was no evidence that gelatine from cattle bones could transmit BSE or nvCJD, the human version of the disease, but the European Scientific Steering Committee has placed restrictions on its use as a precautionary measure.

Stearic acid and magnesium stearate - both animal products - were also used to prevent tablets clumping together.

The report said: "These additives can be derived from animal or vegetable sources and manufacturers rarely say which source they have used."

Insect products

The survey found additives derived from insect secretions and carcasses in several products.

Bee products are also popular in supplements

One such was E120, or cochineal. This is a red dye made from dead cactus beetles and was found in Bassett's Soft and Chewy Vitamins and Sanatogen's one-a-day range.

Additives made from insects have been in use for some years, the survey said.

Shellac is used to add a shine to pills and is made from resinous secretions of tree-dwelling insects in India.

It was found in Minadex chewable children's vitamins, Redoxen slow-release vitamin C, Kwai garlic capsules, Hofels Cardiomax garlic tablets and Seven Seas one-a-day minerals for bones.

Other ingredients

High sodium levels were found in many products to make them fizz.

"Some products, such as the anti-hangover Resolve, warn in the small print that they are unsuitable for sodium-restricted diets, but others, including Boots effervescent vitamin C, give no such warning," the report said.

It also referred to a study performed by the Ministry of Agriculture, Fisheries and Food, which found eight supplements with more than 1mg of lead per kilogram.

It also found two products - Hofels one-a-day garlic with parsley tablets and Wassen's one-a-day garlic tablets - that contained more than 1mg of arsenic per kilogram.

They had 2.2 and 2.1 mg/kg respectively.

The government said it did not believe there was any significant health risk posed by higher than average lead and arsenic levels, but nonetheless asked manufacturers to review their use.

Arsenic is best known as a deadly poison but research published in November showed that it could be useful in cancer treatment.