Claims used to promote some supplements for preventing dementia or aiding brain health are not backed up by scientific evidence, according to a report.
A panel of experts tasked by the watchdog Which? to investigate the science behind a selection of supplements found "no robust evidence" linking ingredients such as Ginkgo Biloba, Vitamin B and D and fish oil to preventing or reducing the risk of dementia.
The panel also warned against using dementia tests after scrutinising a selection ranging from free apps to a £1,275 online test, saying they could lead to many people being unduly worried about the chances of them developing dementia by creating 'false positives'.
Research had shown that many people diagnosed with mild cognitive impairment do not go on to develop dementia at all.
The 'Dementia Test' app failed to ask basic questions such as a person's age and sex, which are the strongest risk factors for dementia and the 'Food for the Brain' app recommended additional tests and Vitamin B, despite those taking the test performing above or at the norm for their age.
The panel, including a GP, a dietitian and a professor of public health medicine, studied a selection of supplements sold on the high-street and online including Bioglan Calamari Gold capsules, Efamol Brain Active Memory capsules, Boots Sharp Mind tablets and BrainSmart Memory capsules.
One claimed the vitamins, minerals and herbal ingredients used could protect against vascular and brain cell damage including strokes, which can cause dementia, while others stated they could maintain brain function, mental performance and memory.
Which? believed that in two cases, the claims were not substantiated by the European Food Safety Authority and were potentially misleading.
Efamol told Which? that it did not intend to mislead consumers and had taken down its website temporarily while undertaking a rigorous review of its marketing and the claims made for its products.
BrainSmart said their product did not claim to prevent, cure or treat disease, and scientific data clearly supported its efficacy, adding that they comply with all applicable rules and regulations.
Which? director of policy and campaigns, Alex Neill, said: "People with dementia, or those with a friend or family member with the condition, will often be scared and worried about their diagnosis.
"It's unacceptable that these companies are preying on people's fears, making claims they simply can't stack up.
"For people worried about dementia our advice is you don't need to spend time and money on expensive supplements or products like online tests or apps.
"There are many alternative sources of free, independent information and advice that can help you to understand your options and next steps."
Which? noted advice that small lifestyle changes could make a difference to the risk of dementia, such as eating a healthy, balanced diet, regular exercise, avoiding high levels of alcohol and everyday activities such as reading and playing chess.
NHS England figures show that more than 750,000 people in the UK suffer from some form of dementia, most commonly Alzheimer's.
A Boots spokeswoman said: "Boots Sharp Mind tablets is a food supplement designed to help support a normal healthy lifestyle and this includes a well-balanced diet.
"The levels of vitamins and minerals present in the product have been reviewed and comply with the safe levels for supplements published by recognised experts. This reference can be found on the Food Standards Agency website and is referred to as 'Expert Group on Vitamins and Minerals (2003) Safe Upper Levels for Vitamins and Minerals'.
"The supplement is not designed to treat or to prevent a diagnosed health condition."