UPDATED: 2.21PM A cluster of dementia cases in a single Ranfurly Shield-winning rugby team have pushed debate about long-term impacts of head injuries back under the spotlight.

An investigation by the New Zealand Herald's found five men from Taranaki's 1964 rugby team have been diagnosed with dementia, and their families are putting it down to various concussions received on the field.

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Auckland University's Professor Thomas Lumley said while the numbers are statistically limited, they do seem to back up anecdotal links, and warrant further study.

"I think these add support for being worried about concussion in rugby, and it's long-term effect," he said.

"What I don't know, having grown up in a non-rugby playing part of Australia, is how much the game has already changed since then."

Lumley said before any conclusions can be drawn, a wider study is needed.

He said something more systematic, like studies done in the US related to football injuries, would give more reliable information, but a cluster gives a starting point of somewhere to look.

ABI Rehabilitation specialist physician Robin Sekerak said there's not enough research, and medical professionals are playing catchup.

"The amount of research with younger persons, adolescence and preadolescence, is really really quite small compared to what we have in adults".