Some 70 per cent of the nation's investment Isa portfolios are in sectors with top risk ratings, according to online investment platform Rplan.co.uk.
And this has created a "major mismatch" between Isas and investors.
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The research found that, on a risk scale of one to seven - where seven is the highest - 12 per cent of UK investment Isa assets are held in sectors rated six and 58 per cent are in sectors rated five.
But Rplan found that just nine per cent of UK adults rate their risk appetites at five or above.
According to the research, UK adults rate their appetite for risk as 2.56 on average. The risk rating of the nation's overall Isa portfolio, meanwhile, is nearly twice as high at 4.82.
Rplan director Nick Curry said: “Many investors in the UK are just not aware of how risky their investments are. Most providers do not display the risk ratings when people are buying funds and even when they are, ratings and other information can be hard to find.
“All fund providers should be displaying the risk levels of their funds clearly, both before and after investing. If necessary, this should be enforced by the regulator.”