High and low vitamin D level is associated with cardiovascular autonomic neuropathy in people with Type 1 and Type 2 diabetes

Aim To investigate the possible association between vitamin D deficiency and cardiovascular autonomic neuropathy in people with diabetes. Methods A total of 113 people with Type 1 or Type 2 diabetes [mean (interquartile range) diabetes duration 22.0 (12–31) years, mean ( sd ) age 56.2 (13.0) years, 58% men] underwent vitamin D (D2 and D3) assessment, and were screened for cardiovascular autonomic neuropathy using three cardiovascular reflex tests [heart rate response to deep breathing (E/I ratio), to standing (30/15 ratio) and to the Valsalva manoeuvre] and assessment of 5‐min resting heart rate and heart rate variability indices. Results We found an inverse U‐shaped association between serum vitamin D level and E/I ratio, 30/15 ratio and three heart rate variability indices ( P < 0.05). Vitamin D level was non‐linearly associated with cardiovascular autonomic neuropathy diagnosis ( P < 0.05 adjusted for age and sex). Linear regression models showed that an increase in vitamin D level from 25 to 50 nmol/l was associated with an increase of 3.9% (95% CI 0.1;7.9) in E/I ratio and 4.8% (95% CI 4.7;9.3) in 30/15 ratio. Conversely, an increase from 125 to 150 nmol/l in vitamin D level was associated with a decrease of 2.6% (95% CI −5.8;0.1) and 4.1% (95% CI −5.8;−0.5) in the respective outcome measures. Conclusions High and low vitamin D levels were associated with cardiovascular autonomic neuropathy in people with diabetes. Future studies should explore this association and the efficacy of treating dysvitaminosis D to prevent cardiovascular autonomic neuropathy.