Lead author, pathologist and biomedical scientist Associate Prof Anitra Carr said the fruits contained vitamin C, which was necessary for the growth, development and repair of all body tissues.
It was also involved in many body functions, including formation of collagen, absorption of iron, the proper functioning of the immune system, wound healing and the maintenance of cartilage, bones and teeth.
Her study analysed about 3000 participants in the 2017-18 United States National Health and Nutrition Examination Survey to see what demographic, lifestyle and health factors affected vitamin C levels.
Results showed men needed about 20% more vitamin C to reach the same circulating level as women.
But it was not due to gender, she said.
Rather, it was because, on average, men weighed and smoked more.
"When we looked at smokers, there was a dose-dependent decrease in vitamin C levels with increasing number of cigarettes smoked per day.
"Furthermore, smokers needed to consume twice as much vitamin C than non-smokers to reach adequate circulating levels of the vitamin.
"And these weren’t necessarily heavy smokers, as the average number of cigarettes smoked per day was less than 10."
Prof Carr said smoking was known to deplete vitamin C levels because of the enhanced oxidative stress it caused in the body.
Since vitamin C was a potent antioxidant, it could scavenge oxidants generated in cigarette smoke, but the vitamin became consumed in this process.
She said body weight also affected vitamin C levels in similar ways to smoking.
"When we looked at the impact of body weight, there was a decrease in vitamin C levels with increasing weight.
"Of note, it was primarily people who weighed less than 60kg who were able to reach adequate circulating levels of the vitamin.
"And, like smokers, people with higher body weight need to consume twice as much vitamin C than people with lower body weight.
"This is particularly important in view of the looming global obesity pandemic."
When people had a higher body weight, the vitamin was diluted into a larger volume, she said.
Additionally, obesity was associated with enhanced inflammation and oxidative stress, both of which could further deplete the vitamin.
"If an intake of 100mg per day — which is approximately the average New Zealand intake of vitamin C — is sufficient for non-smokers and people of lower body weight to reach adequate circulating levels of the vitamin, then smokers and people of higher body weight should aim to consume at least 200mg per day of the vitamin."
About 100mg of vitamin C was contained in one gold kiwifruit or 1.5 oranges.
Eating more vitamin-rich foods or taking supplements was an easy way for people to increase their vitamin C consumption, she said.
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