The study by Consumer Focus Wales found that the elderly, disabled and poorer people were less able to access services since the closures. They also became more isolated and lonely, it added.
Fifty seven post offices in south and west Wales were closed in August 2008 as part of a review by the Post Office Network Change Programme.
"We warned that our local post offices were much more than just shops providing a service," said Preseli Pembrokeshire AM Paul Davies.
South Pembrokeshire AM Angela Burns added: "The social and support aspect provided by small regional post offices was never properly taken into account by the bean counters so these findings come as no great surprise to me or these communities - it was a point we made time and time again in our village halls during all those endless, back-covering consultation exercises."
Maria Battle, senior director of Consumer Focus Wales, said in the report: "Our research shows the real detriment people face, especially vulnerable people, when their local post offices are closed. We found examples of people who relied on public transport or who were elderly or disabled and struggled to access services."
The report said that customers were now facing longer waits and an impersonal service, while those with health problems find it difficult to queue for long periods or to travel the extra distance to the new post office without assistance.
The closure of the local post office also led to far fewer opportunities for social interaction, with people reporting an increase in isolation and loneliness.
"The closure of so many post offices was a real tragedy for Wales and we are only now learning the true social consequences of such action," added Conservative parliamentary candidate Simon Hart.





It looks a bit fishy now, telling us what we already knew. I wonder how hard they really worked to try and help stop these closures?>