Vitamin D Supplementation in Diabetic Nephropathy

Abstract:

Vitamin D has a well-established role in bone health and the prevention of fractures which are associated with increased morbidity and mortality, and reduced quality of life. However, many individuals have sub-optimal vitamin D status (<75nmol/l), and risk increases with geographical location, age, ethnicity, inadequate dietary intake and disease. Diabetes and kidney disease are two chronic diseases associated with both poor bone health and suboptimal vitamin D status. Individuals with diabetes and chronic kidney disease who live in northern Alberta are at a particular risk for suboptimal vitamin D status and poor bone health due to dietary restrictions on vitamin D rich foods (e.g. milk products that are also high in phosphorus and carbohydrates), negligible cutaneous synthesis during the long winter months, and reduced renal capacity to synthesize active vitamin D (1,25(OH)2D). In the general Canadian population, few are able to meet dietary recommendations for vitamin D intake through diet alone and often rely on vitamin D supplements. The need for vitamin D supplementation is increased in diabetics with nephropathy, however the optimal dose and strategy for vitamin D supplementation is unknown. Like other chronic diseases, adherence to therapy is a major issue in this population. With each additional chronic disease an individual has, their adherence to therapy and quality of life decreases. Adherence to vitamin D therapy is known to be particularly poor. This may be related to the silent nature of bone disease, as poor bone health is often not identified until a fracture has occurred. Novel strategies to vitamin D supplementation are needed to prevent poor bone health and fractures, and the resulting decline in quality of life that ensues. Therefore it is important to identify a vitamin D supplementation strategy that increases adherence to vitamin D supplementation and improves vitamin D status and bone health in adults with diabetes and nephropathy.

Objectives:

• Examine the impact of two approaches to oral high dose vitamin D supplementation (2,000 IU/day versus 40,000 IU/month for six months) on overall vitamin D status and markers of bone turnover in adult patients with diabetic nephropathy.
• Examine daily versus monthly vitamin D supplementation strategies in regards to adherence, satisfaction and quality of life in adult patients with diabetic nephropathy.

Hypotheses:

• Vitamin D supplementation (2,000 IU/day and 40,000 IU/month) for six months will result in significantly improved overall vitamin D status and improved markers of bone health in adult patients with diabetic nephropathy.
• Monthly dosing of vitamin D (40,000 IU/month) over six months will result in improved patient adherence and satisfaction with vitamin D supplementation when compared to daily dosing of vitamin D (2000 IU/D). This will improve vitamin D status and bone health parameters, which will result in an increased quality of life and sense of well-being.

Inclusion criteria

• Clinical diagnoses of diabetes (type 1 or 2) and stage 2-4 chronic kidney disease (glomerular filtration rate: 15-89 ml/min/1.73m2)

Exclusion criteria

• Patients with co-morbid conditions known to affect vitamin D metabolism including gastrointestinal, liver, rheumatoid or bone disorders (e.g. hyperthyroidism, untreated celiac disease, cancer, Paget's disease, sarcoidosis, malabsorption, etc). Individuals with severe, permanent vision impairment will be excluded as this will preclude them from reading supplement labels accurately and safely. Pregnant women will be excluded as DXA scans are not recommended during pregnancy. Patients weighing >136kg will be excluded as the DXA table cannot accommodate this weight.
• Patients on drug therapy known to interfere with vitamin D (e.g. oral glucocorticoids, cholestyramine, colestipol, mineral oil, Orlistat, digoxin, antacids).
• Patients with stage 5 CKD (GFR <15ml/min/1.73m2), receiving dialysis or on kidney transplant list.
• Patients with pre-existing hypercalcemia (>2.75mmol/l), hyperphosphatemia (>2.0mmol/l), severe hyperparathyroidism (PTH >600pg/ml), and serum 25(OH)D >200nmol/l.
• Patients with serum 25(OH)D <37.5nmol/l at time of study entry/screening to control for correction of vitamin D deficiency.