An estimated 3 million people regularly take high doses of 100mg-200mg of B6. Most of them are women who claim it helps with menstrual tension, but men at risk from heart disease may take it too. Nutritionists also claim that high doses are useful in treating other conditions, including depression, morning sickness and the side-effects of HRT.
"Our advice is still that the safe level is 10mg", said a spokesman from the Ministry of Agriculture, Food and Fisheries (Maff). Such advice is, however, a climb-down from a year ago when Jeff Rooker, the newly appointed food safety minister, declared that in the light of advice from a scientific advisory committee there was a risk of nerve damage from overdosing. And within a few months the Government was planning to ban the general sale of larger amounts of B6.
This change sparked off a vociferous media and lobbying campaign. Some 110,000 letters were written to MPs and early day motions were signed by an almost unprecedented 200 MPs. In May the decision was looked at again by the Commons agriculture select committee, which roundly condemned the 10mg limit as "scientifically unjustifiable".
"Rooker was furious when we got the committee to take the matter up" declared Christopher Whitehouse, whose company, Good News Communications, handled the parliamentary lobbying.
"Pressure was put on the Labour members to vote against an investigation, but it turned out that one of them regularly took 200mg of B6 daily and another used other supplements, so that was the Labour majority gone."
Out of 49 submissions, 45 opposed the Government's proposal and the committee issued a damning report. They recommended 100mg as a safe level and lambasted Professor Frank Woods, head of the original government advisory committee, as "curt almost to the point of rudeness in responding to articulate and well argued criticisms."
So what is the poor consumer to think? The Committee on Toxicity (COT), consisting of 16 eminent scientists, says 10mg. But the B6 Task Group of 230 British doctors and scientists criticised COT's findings, and the evidence of the US National Academy of Sciences (NAS)' report on B6 involved 50 nutritional and medical experts found no adverse effects below 200mg and recommended a level of 100mg " to be super-safe".
How can experts come to such different conclusions? Partly because of a clash of medical cultures. Traditionally the medical profession has never taken seriously the "supplement and extra vitamins" approach to health. It is frequently said that there is no hard evidence that exceeding the recommended daily allowance does any more than give you very expensive urine.
But, increasingly, research is suggesting that extra supplements can have a protective effect. One, cited in the NAS report, found that not only was B6 effective in reducing heart attacks, but the more you took, the greater the protection, up to about 100 mg. Last year another study found that massive amounts of vitamin E also protected against heart attack.
What is more, the hard evidence for limiting B6 turned out to be shaky. In the end COT's position rested on two cases, both of which were discredited.
All this has raised the issue of the quality of advice that the Government is getting. Lady Mar, a vociferous campaigner on the dangers of organophosphates, feels that the whole system of advisory committees, with senior scientists meeting in private, needs reforming. "The professors are looking for money for research and a major source of funds are the chemical and drug companies. The committee needs to be more open, and drawn from a wider cross-section."
The Group on Vitamins and Minerals, minus Professor Woods, follows exactly these principles, so the B6 debate may yet have a useful ending.