NZ First leader Winston Peters said a 78-year-old woman must have "memory problems", after she challenged the party's record on the cost of living.

Peters read out the woman's social media post at a public meeting in Papakura on Saturday, at the end of an hour-long speech railing against the mainstream media and urging people not to give party votes to National.

He said the woman - whom he called Wendy - had questioned what NZ First achieved over the last three years with National, saying managing on a single pension was "a joke".

The post pointed to higher food and power bills, falling house prices and worsening access to healthcare.

Peters said the message concluded in capital letters: "WHAT HAS NEW ZEALAND FIRST DONE FOR ME?"

"I thought to myself, 'Lady, you're 78 and you've obviously got memory problems'," he said, drawing laughter from the crowd.

Peters responded with a list of policies he credited to his party, including increasing pension payments and scrapping the superannuation surtax.

"A party called New Zealand First got rid of it, abolished the whole lot, that's No.1," he said of the surtax.

He also cited the Gold Card, hearing-aid support and help with winter power bills.

Peters said his party had also insisted on keeping the pension age at 65 and argued against means-testing it.

"Wendy, that's what I've done for you, right? If you've got memory problems, that's why I'm doing it at this meeting - to make sure you've got something to vote on."

He said other parties would turn on young and old people, when they got into trouble.

"One party's been defending the old people of this country, even when its leader was young, thank you very much."