The advert claimed the spread "not only lowers cholesterol but also helps to keep blood vessels healthy", but the ASA ruled the manufacturer did not have enough medical evidence to link the product with healthier blood vessels, deeming the comment to be misleading.
The ASA said the comments implied the product helped maintain healthy blood vessels apart from the cholesterol-lowering benefits, when really the two outcomes were linked.
Unilver said studies it had conducted, as well as external scientific research, "showed the fortification of Flora pro.activ spread with plant sterols, folic acid, vitamins B6 and B12, when combined with the product's low saturated fat and trans fat-free formulation, could help to lower cholesterol and, therefore, keep blood vessels healthy".
But the ASA ruled the firm had breached current advertising codes.
Although the ASA does not have legal powers to ban marketing in breach of the codes, it has asked Unilever to ditch the advert, advising it should, in future marketing campaigns, ensure the public is aware the blood vessel claim has not been individually verified by independent medical experts.
However the manufacturer said it "did not intend to mislead consumers and followed strict internal guidelines before publishing ads". The assertion was a health maintenance claim and the advert did not imply the product could treat, prevent or cure disease, the firm stressed.
The judgement follows last week's upheld complaint against Dairy Crest's television advert for St Ivel "advance" milk. The ad claimed the milk contains the "most effective types of Omega 3" that can advance children's concentration and learning. The firm had based the claim on an Oxford-Durham trial, that showed children with developmental coordination disorder (DCD) benefited from a compound of antioxidants and Omegas 3 and 6.
The ASA said the general claim that St Ivel "advance" milk helped children's concentration and learning had not been established and ruled the advert was in breach of current codes of conduct.
In the past three years Danone, McVitie's and McDonald's advertisements have come under fire from the ASA, which maintains particular health and wellness assertions made in the ads were unverified.
The proliferation of these claims on general foodstuffs reflects the extent of innovation and competitiveness within the functional and health foods market. But while functional food has emerged as a distinct food category, legislation has not yet caught up to reflect this.
"I think maybe because the number of available functional foods is increasing, there might be more cases of this [misleading adverts], but we are not feeling inundated at the moment," said an ASA spokesperson.
EU legislation is currently being developed to harmonise the rules governing the marketing of health benefits of food, only allowing health claims when backed up by medical evidence. Nutritional claims, such as "naturally low in fat", will also be clarified and standardised.
"The codes we administer are not statutory but are underpinned by legislation. They are now in their 11th edition, and run in parallel with the legislation. But the question is, is self-regulation enough?" said the ASA spokesperson.