More than 960 people with diabetes from the United States and Europe were analysed as part of the study, which is believed to be a world first.
"Overall, we’ve found that people with type 2 diabetes have a 1.4 to 1.6-fold higher requirement for vitamin C than those without it, which is a considerable amount," she said.
"The current recommended daily intake for healthy New Zealanders is 40mg of vitamin C.
"But our findings show that people with type 2 diabetes need to increase their vitamin C intake 150% [to at least 125mg per day], to ensure they are getting enough of this essential micronutrient."
People with type 2 diabetes usually had lower levels of vitamin C due to enhanced oxidative stress caused by abdominal fat-related inflammation in the body, she said.
"What’s more, these patients are more prone to experiencing leakage of the vitamin from their kidneys due to diabetic renal dysfunction.
"But what wasn’t known was exactly how much vitamin C they were using or losing as a result of these diabetic complications.
"This study has helped establish that, once and for all."
The research also found the higher the participants’ body weight was, the higher their vitamin C requirements were, which corresponded to an additional required intake of at least 125mg daily.
“There is currently no specific intake category for people with higher body weight internationally, despite the looming obesity pandemic.
"Since higher dietary intakes and circulating concentrations of vitamin C are associated with a lower risk of diabetes morbidity and mortality, increasing intake in people with type 2 diabetes may help slow the progression of their disease and the risk of more severe complications."
She said the findings had important implications for the setting of global vitamin C dietary intake guidelines.
"The introduction of a new vitamin C intake category based on higher body weight or higher BMI would better provide for not only those who are overweight and obese, but also those with type 2 diabetes.
"What we now need are more studies to definitively establish the best method of delivering this extra vitamin C dosage to patients with type 2 diabetes, to ensure their higher needs for this important micronutrient are met."
Several different approaches were available, including increasing the intake of fruit and leafy green vegetables that were high in vitamin C, or taking vitamin supplements, Assoc Prof Carr said.
