Some countries, such as the US, have established a recommended daily allowance for the vitamin but this is based on animal studies looking at prevention of deficiency, conference organiser and antioxidant biochemistry researcher Professor Frank Kelly from King's College London told NutraIngredients.com.
However it is now thought that the vitamin has further benefits to health but there is too few data from human clinical trials to work out how much more people should be taking.
"We really don't have enough information on humans yet to put a number on the amount needed and the type needed," said Professor Kelly.
"To confuse the issue, optimal intake levels are probably different for different people, and to confuse things even further, they are probably different for different forms like natural and synthetic versions," he added.
Professor Kelly said there is a need for long-term (up to 30 years), prospective studies "in which people are taking what we guess now is an adequate amount to maintain optimal health, and then we collate this with disease data".
However with little interest from pharmaceutical companies, apart from those investigating the vitamin as a drug to treat disease, such research is not being done.
"There is a small glimmer of hope that vitamin companies might collaborate on research under an umbrella network, such as something like the EU framework programme," said Kelly.
A number of companies marketing vitamin E supported the New York Academy of Sciences conference, held last month at Tufts University in Boston. It was the first major conference devoted entirely to vitamin E in 15 years.
In this time, studies have both heralded vitamin E as a potent anti-cancer agent and found no evidence to support such an effect, dampening the rapid surge in sales seen in the late 90s. However some companies are reporting renewed growth again - in February Cognis reported that sales of its natural vitamin E surged some 9 per cent last year.
Jeff Hunsicker, vitamin E product manager at conference co-sponsor Cognis Nutrition & Health, said: "The key point about recommended vitamin E intakes that virtually all in attendance agreed on is that the current guidelines are not enough. Optimal intake can help delay or prevent the onset of degenerative diseases."
"It's important to remember that vitamin E is unique in that it is nearly impossible to get enough through a typical diet. That's especially true for those trying to cut out high fats. For example, you'd need to consume bushels of nuts or bottles of oil to equal the amount used in supplements in most of the key studies," he added.
However vitamin E's property as a lipid soluble vitamin raises questions for establishing its potency in humans, noted Professor Kelly.
"Using plasma levels to establish how much of the vitamin the body receives has always been questioned. Plasma levels are closely related to plasma lipid levels - someone may have high plasma levels of the vitamin but also be hypolipidemic," he said."The plasma just carries the vitamin around the body but the real action happens in the tissues. This could be a very important question for future research."
Researchers are also interested in new findings that show the vitamin has many more functions aside from its antioxidant activity.
"The vitamin has now been shown to influence areas without acting as an antioxidant. For instance, it has been found to impact gene production. That was quite a surprise to most people. We are now collecting information on what those genes are and what this means for a cell's ability to deal with a challenge," said Kelly.
"The important thing is you would need very small concentrations to have an impact on genes," he added.
Other issues discussed at the conference included valid biomarkers for vitamin E function in humans and the potency ratio of natural compared to synthetic forms of vitamin E.
A consensus statement of recommendations from a round table held the day before the conference will shortly be submitted to a peer-reviewed journal for publication. The conference conclusions will be published in a book to be released this year.