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Patients living with Type 2 diabetes – and the healthcare professionals caring for them – will now be able to gauge how much vitamin C is needed for daily optimal health, thanks to new research led by a team from the University of Otago, Christchurch.

Anitra Carr imageAssociate Professor Anitra Carr.

Lead author, Associate Professor Anitra Carr, Director of the Christchurch campus’s Nutrition in Medicine Research Group, says the study findings – considered a first – show people with Type 2 diabetes need to consume about 150 per cent more vitamin C than those who don’t have diabetes.

“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, Associate Professor Carr says.

”The current recommended daily intake for healthy New Zealanders is 40 milligrams of vitamin C daily. But our findings show that people with Type 2 diabetes need to increase their vitamin C intake to at least 125 milligrams per day to ensure they are getting enough of this essential micronutrient.”

However Associate Professor Carr says it’s still not known how people with Type 2 diabetes are best able to achieve the higher vitamin C intake needed to maintain optimal levels.

“Fortunately, several different approaches are available, and people with diabetes can discuss their preferences with their health care team.

“Some people may be able to focus on increasing their intake of fruit that is rich in vitamin C, such as oranges. For others who have been advised to moderate their intake of fruit, another approach will be to increase their intake of leafy green vegetables. A third approach, for those using vitamin supplements, is to ensure that the supplement contains a high enough dose of vitamin C to meet daily vitamin requirements,” Associate Professor Carr says.

Although best known for its antioxidant activities, she says there’s been significant interest in the role of vitamin C in both the prevention and treatment of conditions which are potentially modifiable by lifestyle and dietary changes, such as Type 2 diabetes.

“We know that people with Type 2 diabetes usually have lower levels of vitamin C due to enhanced oxidative stress caused by abdominal fat-related inflammation in the body. 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,” Associate Professor Carr says.

The study, published in the international journal Antioxidants, analysed two large international cohort data sets, the US National Health and Nutrition Examination Survey (NHANES) 2017–2018 and the 1993–1997 European Prospective Investigation into Cancer (EPIC)-Norfolk study. The former comprised 2828 adults, 488 (17 per cent) of whom had diabetes; the latter Norfolk study included a further 20,692 participants, 475 (2.3 per cent) of whom had diabetes.

Associate Professor Carr and her team found that participants with diabetes in both studies had a lower vitamin C status than those who were not diabetic, despite both groups having comparable dietary intakes. Furthermore, the higher the participants’ body weight, the higher their vitamin C requirements, corresponding to an additional required intake of at least 125 milligrams 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,” Associate Professor Carr says.

Interestingly, the study authors also found that the blood marker C-reactive protein (CRP), which is a well-known risk factor for cardiovascular disease and corelates strongly with body weight and BMI, showed similar trends. People with high-risk CRP concentrations have a 1.4-fold higher requirement for vitamin C than those with low-risk CRP concentrations (equating to 115 mg/day of vitamin C).

“These findings have 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,” says Associate Professor Carr.

Publication details

Estimating Vitamin C Intake Requirements in Diabetes Mellitus: Analysis of NHANES 201702018 and EPIC-Norfolk Cohorts
Anitra Carr, Helen Lunt, Nicholas Wareham, Phyo K Myint

For more information, contact:

Lorelei Mason
Communications Advisor
University of Otago, Christchurch
Tel +64 21 555 024

Lea Jones
Communications Adviser
Media Engagement
University of Otago
Mob +64 21 279 4969

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