Could screening vitamin C levels improve diabetes outcomes?

Diabetes comes with the risk of a host of health complications. But new Australian research suggests that testing for and addressing a specific vitamin deficiency may help to reduce those risks.
 
That is, vitamin C.
 
Published in Free Radical Biology and Medicine, researchers from Deakin University undertook a comprehensive review of the evidence on vitamin C supplementation, its effects and its potential mechanisms in diabetes management as an adjunct therapy.
 
The authors note that existing evidence shows ‘favourable effects’ of vitamin C on glycaemic control and blood pressure, which may be clinically meaningful, and mixed effects on blood lipids and endothelial function.
 
They also found that emerging evidence for effects of vitamin C supplementation on some diabetes complications, particularly diabetic foot ulcers, is promising.
 
With a high prevalence of vitamin C deficiency among patients with complications, the authors recommend that screening for levels of the vitamin in the blood should become a routine part of clinical diabetes management – and should be the case regardless of whether the person has type 1, type 2 or gestational diabetes.
 
Lead author Dr Shaun Mason is a lecturer in nutrition science at Deakin University’s Institute for Physical Activity and Nutrition. He says the high risk of vitamin C deficiency among people with diabetes is concerning, given the important role the vitamin can play in diabetes management.
 
‘People with diabetes are at high risk of vitamin C deficiency due to a range of factors including higher body needs from oxidative damage, poorer uptake into cells, excessive losses via the kidneys, and insufficient dietary intake,’ Dr Mason said.
 
‘Improving deficient or low levels of vitamin C can improve blood sugar control and reduce risk factors for heart disease such as high blood pressure.
 
‘These beneficial effects might relate to vitamin C supplementation correcting vitamin C deficiency, as well as through the antioxidant effects of vitamin C.’
 
Dr Gary Deed, Chair of RACGP Specific Interests Diabetes and clinical editor of the college’s Diabetes handbook, told newsGP he thinks the research provides an ‘interesting overview’.
 
While he agrees that vitamin C is worth exploring, he says a more person-centred approach is required when it comes to diabetes management.
 
‘Nutritional deficiencies can be mapped in a bi-directional manner to the effects of social inequality and chronic illnesses such as diabetes, as per this focused study on vitamin C,’ Dr Deed said.
 
‘But it is also important to note there are other key nutritional assessments that may be required to assess the person with diabetes’ overall status.’
 
To ensure a fully-person centred approach, the Queensland-based GP says it would be appropriate to have any vitamin or nutritional review ‘done in alignment with a practicing accredited dietitian’s assessment’, and not as a screening of blood testing only.
 
‘The clinical message is that people with diabetes and other chronic illnesses may need timely nutritional assessment, increasingly with onset of complications, including obesity, throughout the management of this illness,’ Dr Deed said.
 
‘Consider nutritional imbalances, deficiencies and excesses (kilojoules or individual supplements) as part of the assessment approach.’
 
In the case that a vitamin C deficiency is identified, and there is a need for supplementation, what is the optimal level required?
 
Dr Mason says further research is still needed to determine this, but he says it is likely that regular use of vitamin C at modest doses such as 500–1000 mg per day could be safely added to diabetes therapies.
 
Like Dr Deed, however, Dr Mason says that a personalised approach is important with individualised advice from a patient’s own doctor before adding supplementation to a management plan.
 
‘This is a strong recommendation for all people with diabetes, but particularly those who have genetic diseases of iron overload, including haemochromatosis, and in those who have impaired kidney function,’ he said.
 
‘A personalised regimen of vitamin C supplementation that considers underlying factors such as a person’s disease status, vitamin C status, and level of diabetes control, is important to help optimise therapeutic effects safely.’
 
Dr Deed agrees, and says it is vital that clinicians first understand the patient’s individual circumstances before making any recommendations, including about supplementation.
 
‘Trying to utilise whole food approaches and also be knowledgeable of the effects of, and safety of, supplementation in the presence of chronic kidney disease, medications, haemochromatosis etc,’ he said.
 
While supplementation can be a faster way to correct a deficiency, Dr Mason highlights that there are a range of vitamin C rich foods that patients can be encouraged to implement into their daily diet to increase levels in the blood.
 
‘Citrus fruits such as oranges, kiwi fruit, berries, and vegetables such as broccoli, cauliflower and cabbage are foods that can be eaten in moderation as part of a well-balanced diet to reduce the risk of vitamin C deficiency,’ he said.
 
Meanwhile, the study author also noted concerns clinicians might have that vitamin C may interfere with blood sugar testing in diabetes patients.
 
But he assures ‘there is no convincing evidence’ for any interference when oral vitamin C supplements are taken at recommended doses.
 
Comprehensive clinical guidance on diabetes and nutrition is available in the Diabetes handbook.
 
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