Claire Forbes, a spokesperson at the ASA, said that the Health & Beauty sector is currently the third most complained about sector after the leisure industry and computing and telecoms.
And in 2001, the agency recorded the highest number of complaints for a supplement that claimed to cause weight loss.
She added that unsubstantiated claims are usually behind the complaints, which come from the public or consumer organisations. Foreign firms also cause a significant number of complaints.
"In an analysis of direct mail advertising, all advertising from abroad broke our rules," said Forbes
The ASA, a self-regulatory organisation that receives around 4000 complaints from all sectors each week, does not have legal powers but can warn a marketer to withdraw advertising. If the warnings, or adjudications, are not adhered to, it can refer the company to the Office of Fair Trading.
ASA can also advise print media in the relevant sector to refuse all advertising from the company.
Earlier this year the ASA contacted manufacturers of bodybuilding supplements, warning them of the legislation covering the advertising of their products.
"We try to establish a level playing field in sectors causing problems," said Forbes.
A special section of the rules, established by the Committee of Advertising Practice (CAP), refers to health products and vitamin and food supplements.
It states that : 'Medical and scientific claims made about beauty and health-related products should be backed by evidence, where appropriate consisting of trials conducted on people. Substantiation will be assessed by the ASA on the basis of the available scientific knowledge.'
It also includes a section on dietary supplements and weight control products, warning that 'testimonials that are not supported by trials do not constitute substantiation'.
The European Commission recently proposed a regulation on nutrition and health claims made on foods, which would also apply to food supplements. Currently under debate by member states, it would introduce severe restrictions on 'slimming' claims and ban those relating to 'wellbeing' and psychological or behavioural functions.