Prospective Evaluation of the Effect of Short-Term Oral Vitamin D Supplementation on Peripheral Neuropathy in Type 2 Diabetes Mellitus

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1 Original Paer Received: December 3, 2013 Acceted: January 18, 2015 Published online: February 26, 2015 Prosective Evaluation of the Effect of Short-Term Oral Vitamin D Sulementation on Periheral Neuroathy in Tye 2 Diabetes Mellitus D. Shehab a Khaled Al-Jarallah a Nabila Abdella a Olusegun A. Mojiminiyi b Hisham Al Mohamedy c Deartments of a Medicine and b Pathology, Faculty of Medicine, Kuwait University, and c Deartment of Medicine, Mubarak Al-Kabeer Hosital, Jabriya, Kuwait Key Words Clinical trial Periheral neuroathy Tye 2 diabetes Vitamin D Abstract Objective: We aimed to assess the efficacy of short-term oral vitamin D sulementation on eriheral neuroathy in atients with tye 2 diabetes. Materials and Methods: This rosective, lacebo-controlled trial included 112 tye 2 diabetic atients with diabetic eriheral neuroathy (DPN) and vitamin D [25(OH)D] deficiency. Patients were sequentially assigned to a treatment grou (n = 57) and a lacebo grou (n = 55). DPN was assessed using a neuroathy symtom score (NSS), a neuroathy disability score (NDS) and a nerve conduction study (NCS). Vitamin D status was determined by measuring the serum total 25(OH)D concentration. Patients received either oral vitamin D 3 casules or starch casules once weekly for 8 weeks. The rimary outcome was changes in NSS and NDS from baseline. The secondary outcome was changes in the NCS result. Results: Serum 25(OH)D concentrations significantly imroved after oral vitamin D sulementation in the treatment grou when comared to the lacebo grou (32.8 ± 23.7 vs. 1.1 ± 3.6, < ). Similarly, the imrovement in NSS values was significantly greater in the treatment grou than in the lacebo grou ( 1.49 ± 1.37 vs ± 0.59, < 0.001). No imrovement was observed for NDS and NCS between the 2 grous after treatment. Conclusion: Short-term oral vitamin D 3 sulementation imroved vitamin D status and the symtoms of neuroathy in atients with tye 2 diabetes. Introduction 2015 S. Karger AG, Basel Diabetic neuroathy is a long-term comlication of diabetes that can cause considerable morbidity in many atients, leading to a deterioration of their quality of life. Previously reorted athways relevant for the develoment of diabetic neuroathy include the glucose flux/ olyol athway (aldolase reductase, sorbitol), the hexosamine athway (fructose-6p), the accumulation of advanced glycation end-roducts and several other mecha- karger@karger.com S. Karger AG, Basel /15/ $39.50/0 This is an Oen Access article licensed under the terms of the Creative Commons Attribution-NonCommercial 3.0 Unorted license (CC BY-NC) ( alicable to the online version of the article only. Distribution ermitted for non-commercial uroses only. Prof. D. Shehab Faculty of Medicine, Kuwait University PO Box Jabriya, Safat (Kuwait) hsc.edu.kw

2 Diabetic atients screened n = 228 NSS, NDS, NCS, 25(OH)D Assessed for eligibility n = 117 Excluded Normal vitamin D n = 16 Normal NCS n = 63 Drugs n = 2 Renal/heatic failure n = 9 Malignancy n = 1 Droouts n = 20 NSS, NDS, NCS Droouts n = 2 Treatment grou with oral vitamin D n = 59 Placebo grou n = 58 Droouts n = 3 Fig. 1. Flow chart. Comleted 8 weeks n = 57 Comleted 8 weeks n = 55 nisms [1]. A deficiency of vitamin D [25-hydroxyvitamin D, 25(OH)D] is common in atients with diabetes, and low concentrations are associated with the resence and the severity of sensory neuroathy in diabetes [2, 3]. The mechanisms and athohysiology of neuroathy are associated with hyerglycemia via microvascular injury or direct neuronal metabolic injury [2]. Vitamin D deficiency has been shown to be an indeendent risk factor for diabetic eriheral neuroathy (DPN) [3, 4]. Toical and oral vitamin D have been reorted to significantly reduce the symtoms and ain of DPN [5 7]. However, no casecontrol clinical trials have been reorted that demonstrate the efficacy of vitamin D sulementation on the symtoms of DPN. We hyothesized that correction of a vitamin D deficiency may directly or indirectly imrove the symtoms of DPN. This study evaluated the otential efficacy of short-term oral vitamin D sulementation on neuroathy in atients with tye 2 diabetes mellitus, making use of validated neuroathy assessment tools: a neuroathy symtom score (NSS), a neuroathy disability score (NDS) and electrohysiological studies, i.e. a nerve conduction study (NCS). Materials and Methods Study Design This study involved an interventional, rosective, nonrandomized, double-blind, lacebo-controlled clinical trial lasting 8 weeks. It assessed, by means of an NSS, an NDS and an NCS, the efficacy of vitamin D sulementation on subjective and objective neuroathic manifestations in atients. Patients who fulfilled the inclusion criteria were recruited by indeendent clinicians from hosital diabetology clinics ( fig. 1 ), and were then allocated to the 2 arms of the intervention, i.e. treatment and lacebo, according to a sequential order generated by the hosital recording system. Particiants Exclusion Criteria These included: atients with a nondiabetic cause for neuroathy such as inflammatory rheumatic diseases, malignancy, hyerarathyroidism, alcoholism, renal or liver failure or vitamin B 12 deficiency, atients taking drugs that could cause eriheral neuroathy and atients with other causes for ain in the feet (eriheral arterial disease or infections). Inclusion Criteria Adult atients with tye 2 diabetes with DPN and vitamin D deficiency were eligible. In total, 228 tye 2 diabetic atients were screened over a 1-year eriod from March 2012 to March 2013; 111 were excluded ( fig. 1 ), and of the remaining 117, 59 were assigned to treatment and 58 to lacebo. Two atients droed out of the treatment grou and 3 out of the lacebo grou. So, 57 atients in the treatment grou and 55 in the lacebo grou with DPN and vitamin D deficiency comleted the study, i.e. a total of 112 atients (48 males and 68 females) with an age range of years. Tye 2 diabetes was defined as a fasting lasma glucose level 7.0 mmol/l on at least two occasions or glycated hemoglobin (HbA1c) 6.5% [8]. All atients attended regular follow-us at the diabetic clinics of the Mubarak Al-Kabeer Hosital, Kuwait. A detailed history was recorded and a hysical examination was conducted for all atients. Fasting blood glucose, renal, liver and liid rofiles and HbA1c were measured. The 25(OH)D level was also measured. Vitamin D deficiency was defined as a serum 25(OH)D con- 2 Shehab/Al-Jarallah/Abdella/Mojiminiyi/ Al Mohamedy

3 Table 1. Demograhic characteristics of tye 2 diabetic subjects in the treatment and lacebo grous at baseline Characteristics Treatment grou (n = 57) Placebo grou (n = 55) value Gender Male 21 (36.8) 27 (49.1) Female 36 (63.2) 28 (50.9) Mean age ± SD, years 61.8 ± ± Range Duration of diabetes >10 years 44 (77.2) 35 (63.6) <10 years 13 (22.8) 20 (36.4) Body mass index <25 8 (14.0) 4 (7.3) >25 49 (86.0) 51 (92.7) Retinoathy Positive 20 (46.5) 12 (33.3) Coronary heart disease Positive 16 (32.7) 10 (24.4) Stroke Positive 2 (3.6) 1 (2.3) Treatment OHA only 20 (35.1) 25 (45.5) Insulin only 6 (10.5) 4 (7.3) Insulin + OHA 31 (54.4) 26 (47.3) Values denote n (%), unless otherwise indicated. OHA = Oral hyoglycemic agent. centration of <50 nmol/ml. Written informed consent was obtained from all articiants. The study rotocol was aroved by the Ethics Committees, Faculty of Medicine, Kuwait University, and the Ministry of Health, in accordance with the rovisions for human research in the Declaration of Helsinki. The study subjects were drawn from the general oulation living in Kuwait, a geograhic region which is sunny all the year round and where the majority of citizens have a dress code of covering u. Study Outcomes The rimary outcome measures were the assessment of neuroathy using an NSS and an NDS. The NSS includes symtoms of neuroathy (the nature of ain, the location, the duration and the measures undertaken to alleviate symtoms). Generally, the NSS values ranged from 0 to 9, and a value >5 was defined as neuroathy. The NDS includes ankle reflex, vibration, inrick and temerature; its values ranged from 0 to 10, and a value >6 was defined as neuroathy [3, 9 11]. The secondary outcome measure was the assessment of neuroathy by means of an NCS, erformed on all atients using established, standard techniques [12, 13]. Measurements of latencies, amlitudes and conduction velocities were evaluated using reviously established cut-off values, for the motor (eroneal, tibial, median and ulnar) and sensory (sural, median and ulnar) nerves [3, 14, 15]. The clinical assessment of eriheral neuroathy at baseline and after treatment was conducted for all atients by a single clinician (D.S.) who was blinded to the treatment choice. Thus in this study, tye 2 diabetic atients who had an NSS >5 and an NDS >6, in addition to an abnormal NCS, were categorized as having DPN. Serum Vitamin D Status Vitamin D status was determined at baseline and after treatment by measuring serum total 25(OH)D concentrations using radioimmunoassay kits (DiaSorin, Stillwater, Minn., USA) according to the manufacturer s instructions. A serum 25(OH)D concentration <50 nmol/ml was defined as a vitamin D deficiency [16]. Intervention Concealed oaque enveloes were reared for all study articiants for allocation into the vitamin D treatment grou or the lacebo grou. This was done under the direct control of a single investigator (H.M.). The treatment grou received oral casules of vitamin D 3 (a casule of cholecalciferol, 50,000 IU, Bronson, Lindon, Utah, USA) once weekly for 8 weeks [17]. The lacebo grou received starch casules, also once weekly for 8 weeks. The study medications were visually indistinguishable from one another and were stored as advised by the manufacturers. The study articiants and the outcome assessor were blinded to the treatment allocation once during the conclusion of the study. Primary and secondary outcome measures of all atients were reassessed after 8 weeks of intervention. Clinical Evaluation The rimary end oint was the difference between baseline and after treatment in the NSS and NDS, and the secondary end oint was changes in the electrohysiological study, i.e. the NCS, between baseline and after treatment. Comliance with sulementation was evaluated by reeating laboratory tests. Indirect measures to imrove the adherence to interventions included educating the atients and scheduling aointments. Statistical Analysis Data were analyzed using the Statistical Package for Social Sciences version 19.0 (SPSS Inc., Chicago, Ill., USA). Data are exressed as ercentages or mean ± SD. Categorical variables were comared by χ 2 test. The mean values of the continuous variables were comared using the indeendent-samles or aired-samles Student t test as aroriate. For skewed data, analysis was erformed using the Mann-Whitney U test. The Searman correlation coefficient was used to evaluate the correlation between the imrovement in 25(OH)D and the NSS. Values of < 0.05 were considered to be statistically significant. Results The demograhic characteristics of the 2 grous at baseline are given in table 1. There were no significant differences between the 2 grous regarding gender, age, duration of diabetes, body mass index, the comlications of diabetes (retinoathy, coronary heart disease and stroke) or antidiabetic medications. The biochemical a- Oral Vitamin D in Diabetic Neuroathy 3

4 Table 2. Metabolic arameters of the treatment and lacebo grous at baseline (before treatment) and after treatment Parameters Treatment grou (n = 57) Placebo grou (n = 55) value HbA1c, % Before 9.2 ± ± After 9.5 ± ± Creatinine, μmol/l Before 68.6 ± ± After 69.3 ± ± Total cholesterol, mmol/l Before 4.5 ± ± After 4.6 ± ± Triglycerides, mmol/l Before 1.6 ± ± After 1.7 ± ± HDL-C, mmol/l Before 1.1 ± ± After 1.0 ± ± LDL-C, mmol/l Before 2.6 ± ± After 2.7 ± ± Serum calcium, mmol/l Before 2.4 ± ± After 2.3 ± ± Serum albumin, g/l Before 37.4 ± ± After 37.8 ± ± AST, IU/l Before 22.7 ± ± After 23.8 ± ± ALT, IU/l Before 24.3 ± ± After 23.2 ± ± ALP, IU/l Before 83.5 ± ± After 79.0 ± ± Values reresent mean ± SD. ALP = Alkaline hoshatase; ALT = alanine transaminase; AST = asartate transaminase; HDL- C = high-density liorotein cholesterol; LDL-C = low-density liorotein cholesterol. rameters of the treatment and lacebo grous at baseline and osttreatment are given in table 2. No significant difference was observed in glycemic control between the 2 grous, demonstrated by the HbA1c values (9.5 ± 2.1 vs. 8.9 ± 2.1%, > 0.05). There were no differences in other metabolic arameters measured at baseline and after treatment between the two grous. The baseline and follow-u NSS and NDS values and the vitamin D status before and after treatment for both study arms are shown in table 3. Of the 57 atients in the Table 3. Baseline and follow-u values and comarison of differences in NSS, NDS and vitamin D status before and after treatment between the treatment and lacebo grous Parameters Before After Differences 1 value NSS Treatment 5.92 ± ± ± 1.37 <0.001 Placebo 5.50 ± ± ± 0.59 NDS Treatment 8.4 ± ± ± Placebo 7.8 ± ± ± (OH)D, mmol/l Treatment 25.3 ± ± ± 23.7 < Placebo 29.2 ± ± ± 3.6 Values reresent mean ± SD.The Mann-Whitney U test was used. 1 The minus sign indicates that the values decreased after treatment. treatment grou, 38 (66.7%) had normal 25(OH)D levels after the treatment eriod. The differences in the NSS, NDS and vitamin D status before and after treatment were used to comare the effect of vitamin D sulementation between the treatment and lacebo grous. The reduction in the NSS values after treatment was significantly more in the treatment grou than in the lacebo grou ( 1.49 ± 1.37 vs ± 0.59, < 0.001), while no difference was noted for the NDS. Similarly, the imrovement in the serum 25(OH)D concentration after treatment was extremely significant in the treatment grou comared to the lacebo grou (32.8 ± 23.7 vs. 1.1 ± 3.6, < ). The Searman correlation did not reveal any significant correlation between change in 25(OH)D and imrovement in NSS (rho = 0.052, = 0.702) The NCS data on the latency, amlitude and conduction velocity for the motor and sensory nerves in both grous after the 8-week treatment eriod are given in table 4. The baseline and follow-u results for the normal cut-off values for the eroneal and sural nerves including distal latencies, conduction velocities and amlitudes showed no statistical difference between the grous during the study eriod ( table 5 ). Changes in NCS in both grous after treatment were not significant. Only 1 atient had a normal NCS result (0.89%) after 8 weeks and 3 atients in the treatment grou (2.6%) showed an imrovement after the vitamin D treatment. No changes were observed in the NCS in the lacebo grou. 4 Shehab/Al-Jarallah/Abdella/Mojiminiyi/ Al Mohamedy

5 Table 4. NCS data including cut-off values for the treatment grou and the lacebo grou after treatment Table 5. Comarison of NCS data on the eroneal and sural nerves before and after treatment in the treatment and the lacebo grou Treatment grou (n = 57) Placebo grou (n = 55) Normal cut-off values value 1 Before treatment After treatment Normal cut-off values value 1 Distal latency, mv Median motor 4.5 ± ± 2.4 < Median sensory 3.1 ± ± 0.7 < Ulnar motor 2.6 ± ± 0.1 < Ulnar sensory 2.7 ± ± 0.2 < Peroneal motor 5.2 ± ± 1.0 < Tibial motor 4.9 ± ± 0.6 < Sural sensory 3.3 ± ± 0.3 < Conduction velocity, m/s Median motor 44.0 ± ± 9.1 > Median sensory 48.0 ± ± 12.7 > Ulnar motor 52.0 ± ± 1.4 > Ulnar sensory 52.8 ± ± 1.4 > Peroneal motor 37.0 ± ± 11.5 > Tibial motor 44.0 ± ± 9.6 > Sural sensory 41.4 ± ± 3.1 > Motor amlitude, mv Median 5.9 ± ± 4.0 > Ulnar 8.5 ± ± 0.7 > Peroneal 2.2 ± ± 1.9 > Tibial 5.9 ± ± 3.4 > Sensory amlitude, μv Median 17.2 ± ± 7.0 > Ulnar 17.6 ± ± 0.1 > Sural 5.9 ± ±.2.4 > Distal latency, mv Peroneal motor <5.6 Treatment 5.3 ± ± Placebo 4.9 ± ± Sural sensory <3.5 Treatment 3.4 ± ± Placebo 3.4 ± ± Conduction velocity, m/s Peroneal motor >40 Treatment 36.1 ± ± Placebo 43.2 ± ± Sural sensory >40 Treatment 41.0 ± ± Placebo 39.1 ± ± Motor amlitude, mv Peroneal motor >1.5 Treatment 2.0 ± ± Placebo 2.9 ± ± Sensory amlitude, μv Sural sensory >9 Treatment 6.3 ± ± Placebo 6.4 ± ± Values reresent mean ± SD. 1 Paired-samles t test. Values reresent mean ± SD. 1 Indeendent-samles t test. Discussion In this study, oral sulementation of a dose of cholecalciferol (a 50,000-IU casule) once weekly for 8 weeks was associated with a significant imrovement in the 25(OH)D concentration in the treatment grou comared to lacebo. The imrovement in NSS was also significant in the treatment grou comared to the lacebo grou. No imrovement in NDS or NCS result was observed in either grou after vitamin D sulementation. These findings are consistent with our revious study [3] which reorted vitamin D as an indeendent risk factor in eriheral neuroathy in atients with tye 2 diabetes. This study has thus established that oral vitamin D sulementation corrects vitamin D deficiency, which leads to an imrovement in the symtoms of neuroathy. The main symtom imrovement observed was in the sensation of neuroathic ain, esecially burning/hyeresthesia. However, it is not clear whether this was because of an elevation of ain threshold or due to an imrovement in the function of the affected nerves, or both [7, 18]. Vitamin D is a otent inducer of neurotrohins and neurotransmitters; the biological effect of vitamin D on the nervous system includes the biosynthesis of enzymes involved in neurotransmitter synthesis as well as substances involved in brain detoxification athways. The addition of vitamin D otentiates the nerve growth factor (NGF), a rotein required for the develoment and maintenance of several oulations of neurons in the eriheral nervous system [19]. In animal studies, it has been shown that the addition of vitamin D 3 analogs otentiates the reversal of the neurotrohic deficits of diabetes [20, 21]. However, the mechanisms to exlain the observed symtomatic imrovement in humans are yet to be elucidated. It has been reorted that vitamin D analogs are also effective in inducing NGF in human cell lines [22, 23]. In the skin, eidermal keratinocytes are the rimary source of NGF and decreased NGF in atients with diabetic olyneuroathy correlates with neuroath- Oral Vitamin D in Diabetic Neuroathy 5

6 ic indicators of sensory and autonomic nerve function [23]. No significant changes were observed in NDS (ankle reflex, inrick or vibration), robably due to an inadequate dose or duration of sulementation or both. The majority of our atients did not show an imrovement in NCS with treatment. This could also be due to the underlying athohysiology of eriheral neuroathy in diabetes, since the duration of diabetes in our atients was rolonged (years) and the athohysiology of neuroathy could be mainly axonal; it takes longer than 8 weeks for nerves to be regenerated or to correct the effects of an absence of vitamin D. Only 1 (0.89%) atient had a normal NCS result after 8 weeks and 3 (2.6%) showed an imrovement after treatment, observed in the motor conduction velocity of the eroneal and tibial nerves and the sensory conduction velocity in the sural nerves. The NCS was conducted by the same clinician using the same machine and standard techniques, so the likelihood of technical bias was reduced. Interestingly enough, in animal models of diabetes [21], no changes were observed in the motor or sensory conduction velocities after 8 weeks of treatment with a vitamin D 3 derivative. It is, therefore, temting to seculate that the human and animal exerimental findings were comarable. The effects observed in this study were not biased by any changes in glycemic control, since no significant differences were noted between the treatment and lacebo grous in HbA1c before or after treatment. A randomized, lacebo-controlled, double-blind study [5] that used a toical cream containing vitamin D 3 in 34 tye 1 and tye 2 diabetic atients led to an imrovement in symtoms and quality of life. In a study by Lee and Chen [6], 51 tye 2 diabetic atients with neuroathic ain and vitamin D deficiency were treated with oral vitamin D 3, and then reevaluated after 3 months. They showed an imrovement on a visual analog scale. The most recent similar account was a case reort by Bell [7], where oral vitamin D sulementation, even in a tye 1 diabetic atient, led to a dramatic imrovement in neuroathic symtoms. The main limitation of this study was the nonrandomization of the selection of atients. However, there were also several strengths: it was a rosective, lacebo-controlled, double-blind study with a large samle. Two reviously validated neuroathic scores, namely the NSS and NDS as rimary outcome measures and an NCS as a secondary outcome measure, were used. Conclusions This study showed that short-term oral sulementation of vitamin D to correct a deficiency imroved the symtoms of eriheral neuroathy in atients with tye 2 diabetes. We recommend conducting randomized, controlled trials in order to exlore, rosectively, the issues of roer dosing as well as the route and duration of treatment, to confirm the efficacy and clinical benefits of vitamin D sulementation on DPN. Acknowledgement We would like to thank Dr. Mini Abraham Puliyelil for technical assistance. Disclosure Statement The authors have no conflicts of interest to disclose. References 1 Edwards JL, Vincent AM, Cheng HT, et al: Diabetic neuroathy: mechanisms to management. Pharmacol Ther 2008; 120: Chaychi L, Mackenzie T, Bilotta D, et al: Association of serum vitamin D level with diabetic olyneuroathy. Med Pract Rev 2011; 2: Shehab D, Al-Jarallah K, Mojiminiyi OA, et al: Does vitamin D deficiency lay a role in eriheral neuroathy in tye 2 diabetes? Diabet Med 2012; 29: Soderstrom LH, Johnson SP, Diaz VA, et al: Association between vitamin D and diabetic neuroathy in a nationally reresentative samle: results from NHANES. Diabet Med 2012; 29: Valensi P, Devehat C, Richard J, et al: A multicenter double blind, safety study of QR-333 for the treatment of symtomatic diabetic eriheral neuroathy: a reliminary reort. J Diabetes Comlications 2005; 19: Lee P, Chen R: Vitamin D as an analgesic for atients with tye 2 diabetes and neuroathic ain. Arch Intern Med 2008; 168: Bell DS: Reversal of the symtoms of diabetic neuroathy through correction of vitamin D deficiency in a tye 1 diabetic atient. Case Re Endocrinol 2012; 2012: Standards of Medical Care in Diabetes Diabetes Care 2013; 36(sul 1):S11 S66. 6 Shehab/Al-Jarallah/Abdella/Mojiminiyi/ Al Mohamedy

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