Background:
Vitamin D deficiency is considered a risk factor for schizophrenia spectrum disorders. The influence from vitamin D may be specifically important in the developing fetal brain. However, vitamin D deficiency is also found to be associated with symptom severity in established schizophrenia spectrum disorder, indicating that vitamin D also plays an important role in the adult brain. Our research group has found a strong association between low vitamin D levels and higher symptom burden of depressive- and negative symptoms, and associations between vitamin D deficiency and cognitive impairments, reduced processing speed in particular. Our results are in line with results from other studies. Symptoms of vitamin D deficiency per se involves motor fatigue and muscle weakness, and vitamin D is found to be crucial for the connectivity in neuronal circuits responsible for both locomotor-, emotional- and reward dependent behavior. Despite the strong associations between vitamin D deficiency and core features of schizophrenia spectrum disorders, very few intervention studies have been performed in schizophrenia samples.
The cognitive impairment of reduced processing speed is evaluated by standardized cognitive tests. The task could be to match symbols and letters by writing on a sheet of paper, to draw a pattern or solve a puzzle. The ability to perform will thus be dependent on the actual physical speed, the interaction between brain activity and body movements, i.e. psychomotor function, and cognition. In this study we will therefore investigate vitamin D's effect om cognitive processing speed and the effects on other outcomes related to psychomotor function. We will use both well-known clinical methods as well as new digital measures to measure potential effects.
Sociodemographic and diagnostic assessments:
Age, sex, cultural background, education level, work-, and civil status will be mapped by a structured interview and by information obtained from patient records. The Structured Clinical Interview for DSM-5 Disorders, Clinician Version (SCID-5 CV) will be used for diagnostic purposes. Current medication will be registered by interview or obtained from patient records.
MinDag Smart phone application:
Participants will be asked to use the smart phone application MinDag (MyDay) during the 12 week trial period, and download the app to their own smartphone. MinDag was developed by a team of clinical researchers at Norment in collaboration with the Web-app group at the Oslo University Center for Information Technology (USIT). The final version is now implemented at the Norment center. The app consists of daily self-reports covering activities/functioning, and a biweekly module assessing negative symptoms.
Actigraph:
The participants will also be asked to wear a MotionWatch 8 actigraph from CamNtech, which will yield continuous measures of body acceleration. Actigraphs have proven to be important ambulatory tools to obtain objective measures of sleep and activity. However the main focus for the use of the actigraph is to measure body acceleration, i.e. physical activity. The MotionWatch 8 is CE-marked, waterproof and has a battery lives of approximately 3 months. Actigraphs have successfully been used in studies of schizophrenia spectrum disorders to investigate sleep patterns and physical activity.
Medical product and placebo:
Vitamin D3 supplements as oral capsules will be used for supplementation, with a dosage of 50 microgram (= 2000IE) daily. This dosage have not been associated with negative effects in former intervention studies and is considered sufficient to ensure significant increase in S-25(OH)D. Norwegian Scientific Committee for Food and Environment has proposed 100 microgram (= 4000IE) daily as upper tolerable intake limit for vitamin D substitution. To make sure the study participants do not risk intoxication we have chosen to dosage the vitamin D supplementation with half the dosage for non- tolerable dose.
Vitamin D is considered as a food supplement, not a medical drug. The research protocol has been submitted to the Norwegian Medicines Agency, who has concluded that the project is not categorized as a medical drug study.
Vitamin D measurements:
S-25(OH)D is perceived as a satisfactory indicator of the vitamin D level in the body and is the metabolite that will be measured and used in the analyses. Serum concentration of 25(OH)D reflects both vitamin D produced from the skin and that obtained from food and supplements. The half-life of S-25(OH)D is several weeks and S-25(OH)D is perceived as a satisfactory indicator of the vitamin D level in the body.
Statistics:
The main analyses will be performed in IBM SPSS Statistics for investigating group differences (T-test, ANOVA and regression models will be used for this purpose), and change form baseline to follow up (mixed models will be the preferred analytic model here). The biostatistical work group at the Norment center will be conferred for the statistical analyses, for analyzing data from the app and actigraph in particular. Possible confounders known from the literature will be controlled for, such as gender, age, cultural background and current medication.
Sample size calculation:
We assume that the primary outcome (results from digit symbol coding) is a continuous variable with a normal distribution. Two independent clinical groups will be compared. In a similar sample (participants with a psychotic disorder), the results showed mean value 53.06 and standard deviation 11.26 in digit symbol coding for participants with vitamin D level ≥25 nmol/L and mean 45.65 and standard deviation 9.58 in participants with vitamin D level \< 25 nmol/L. This was a significant difference with t-test, t=3.59 (95% confidence interval 3.35-11.47), p\<0.001 and estimated effect size Cohen's d= 11.42. With significant level set to give a statistical power of 0.80 and alpha of 0.05 and with the same anticipated group differences in mean and standard deviations in the treatment group versus the placebo group, sample size calculation indicate that a number of 76 participants (N= 38 in each group) will be sufficient. However, we expect around 15 % drop out rate and we therefore aim to include 90 participants (N= 45 in each group).
User involvement:
This project has had active user involvement since the planning of the project. There has been regular meetings over the last year between the PI and the user representatives. The formulation of the written consent and information material for participants are developed in collaboration with the user representatives. The current research protocol has been presented to the user representatives and they have provided relevant feedback. They support the project and find the project relevant for the target group, particularly as the project can highlight a treatment for better well-being, as well as contributing to increased knowledge in the field.
