Nelson Marlborough District Health Board principal dental officer Dr Rob Beaglehole, left, and chief executive Chris Fleming in the Nelson Hospital cafe with some of the diet soft drinks and fruit juices that will no longer be available at hospital cafes, shops and vending machines from May 1.

Diet soft drinks, juices, flavoured water and smoothies will be removed from the shelves and hospital menus at Nelson and Wairau Hospitals in a move that is believed to be the first of its kind in New Zealand.

The crackdown on sugary drinks will see patients and visitors to Wairau Hospital, in Blenheim, choose between milk, water, tea and coffee.

An existing Nelson Marlborough District Health Board policy preventing the sale of sugar-sweetened beverages was extended to cover artificially-sweetened beverages, flavoured water, smoothies and juices at a health board meeting in Nelson on Tuesday.

Those drinks would no longer be served to patients or sold from cafes, shops and vending machines at Wairau Hospital and Nelson Hospital from May 1.

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Nelson Marlborough was the first health board in New Zealand to introduce limits on sugary drinks.

The updated policy means no pre-packaged drinks containing sugar will be available on health board sites.

Nelson Marlborough District Health Board principal dental officer Dr Rob Beaglehole said, to the best of his knowledge, Nelson Marlborough was the only health board in New Zealand to ban artificially-sweetened beverages, as well as juices and smoothies.

"It's exciting because once again Nelson Marlborough District Health Board is leading the way.

"We'd like to see other district health health boards following suit."

The policy was about being a good role model and showing leadership as a health board, Beaglehole said.

"It might seem quite radical but the same thing was said two years ago when we got rid of sugar-sweetened beverages.

"Overwhelmingly the response has been positive."

The board originally moved to ban sugar-sweetened beverages in 2014 to recognise their effect on oral health, and their role in obesity and type 2 diabetes.

However, Beaglehole said artificially-sweetened beverages, smoothies and juices also had a detrimental effect on teeth and general health.

One small smoothie Beaglehole found in the cafe at Nelson Hospital had 14 teaspoons of sugar.

The World Health Organisation recommended adults had no more than six teaspoons of sugar per day, while children should have no more than three.

"A lot of people don't understand that these products are so sugar-laden.

"If a child had one of those smoothies with 14 teaspoons of sugar that's almost five days of sugar in one hit."

Artificially-sweetened beverages, smoothies and juices encouraged sugar cravings, and sugar dependence, he said.

High levels of acidity in the drinks caused dental erosion.

Diet drinks had no nutritional value and displaced healthier drink choices, including milk and water.

There was also emerging evidence that artificially-sweetened beverages could cause weight gain, Beaglehole said.

A study that followed 3600 people for seven years found those who drank diet soft drinks had a 50 per cent higher increase in their body mass index than those who did not.

People were still able to bring sugary beverages into the hospital and sugar would still be available at the cafes for those wanting to add it to their tea or coffee.

"The policy doesn't ban drinking sweet drinks, it only prevents people from buying them at the hospital," Beaglehole said.

"As a hospital we don't believe we should be selling sickness."