People with diabetes should receive cholesterol-busting drugs regardless of whether they have signs of heart disease, UK researchers say.
Millions of statins are prescribed annually in the NHS
Statins cut the risk of heart attack, stroke and death in diabetic people even in those with low cholesterol levels, analysis of 14 trials shows.
It means hundreds of thousands more people could benefit from treatment, the Lancet report said.
There are 2.5 million people diagnosed with diabetes in the UK.
Many more do not realise they have the condition and statins are "underused" in people with diabetes the researchers said.
Guidance from the National Institute of Clinical and Health Excellence (NICE) in England and Wales issued in 2006 estimated around 3.3 million people are eligible for treatment with statins.
This includes people with diabetes who have a 20% risk of developing cardiovascular disease in the next 10 years.
A team of researchers at Oxford University reviewed studies of more than 90,000 people - 19,000 with diabetes - and found that many more would benefit from statins than previously realised.
They found that standard daily treatment with statins would prevent about one third of heart attacks and strokes in people with diabetes.
The benefits were seen regardless of age, sex and whether patients were already showing signs of cardiovascular disease.
After five years, 42 fewer people with diabetes had major problems, such as heart attacks or stroke, for every 1,000 treated with statins.
The only exceptions for treatment should be those with exceptionally low risk, such as children or those who cannot take the drugs for other reasons, such as pregnant women.
Study leader Professor Colin Baigent said there had been some debate about whether statins would have the same benefits in people with diabetes as those with heart disease in general.
"People with diabetes are a clearly defined group of people at an increased risk of cardiovascular disease.
"What we're saying is statins are clearly effective in every type of person with diabetes."
Diabetes UK estimates 60% of all diabetics currently receive statins. That would mean the vast majority of the remaining 40% could also benefit from these drugs, according to the researchers.
However, Douglas Smallwood, chief executive of Diabetes UK, recommended statins for people with diabetes over the age of 40 or diabetics younger than 40 with another risk factor.
"Diabetes UK also strongly recommends that good diabetes management should rely not only on medication, but also on a healthy lifestyle and diet," he added.