Discussion
low back pain, pain
RHEUMATOID ARTHRITIS, OSTEOARTHRITIS, FIBROMYALGIA, VITAMIN D DEFICIENCY, CHRONIC PAIN
In this large RCT, supplementing older adults with 60 000 IU of vitamin D/month did not influence pain. This finding was consistent in all subgroups and at all time points.This analysis has a number of strengths. It was nested in a large population-based RCT with a long intervention period, providing information to inform population-level interventions. The large monthly dose of vitamin D caused a substantial difference in 25(OH)D concentration between the study groups and adherence to the intervention was high. The lack of a baseline PIQ-6 measure is a limitation. However, all other characteristics, including a history of chronic pain, were well balanced at baseline, suggesting this would have also been the case for PIQ-6 scores. Further there was little difference in the percentage with missing PIQ-6 data between study groups, and the PIQ-6 score at year 1 was minimally associated with missing PIQ-6 at subsequent time points. Thus, the results are unlikely to be biased by differential withdrawal.The prevalence of bodily pain among the participants included in this analysis was comparable to the Australian population. In the 2011–2012 Australian Health Survey approximately three-quarters of people aged 65–74 reported experiencing pain of any severity in the 4 weeks prior to interviewThe lack of effect of vitamin D supplementation on pain is consistent with the findings of a similar trial from New ZealandOur null finding is also supported by several systematic reviews and meta-analysesThe D-Health and ViDA Trials used monthly bolus doses of vitamin D. It is possible that bolus dosing confers less benefit than daily dosing, even though it results in a similar 25(OH)D concentrationWe used a questionnaire instrument that measures overall bodily pain and the impact of the pain. It is possible that vitamin D has effects on pain with specific underlying causes, such as fibromyalgia, which may be under-represented in the study population. However, the strong associations with known risk factors suggest that the PIQ-6 is a robust measure of overall pain, and it is reasonable to conclude that there is no impact on pain arising from the most common causes in older people (i.e. osteoarthritis, rheumatoid arthritis, osteoporosis)Vitamin D supplementation may only be of benefit for pain in people who are vitamin D deficient, but this has not been adequately explored. One RCT found significant improvement of low back pain only in patients with serum 25(OH)D concentration <30 nmol/l, after a bolus oral dose of 100 000 IU followed by 4000 IU/day of vitamin D supplementation, but in the ViDA Trial there was no evidence of benefit in participants with serum 25(OH)D concentration < 50 nmol/lThe mean concentration of serum 25(OH)D in our study population was somewhat higher than in the Australian general populationIn conclusion, this analysis of a large population-based trial suggests that vitamin D is unlikely to have any clinically relevant effect on non-specific pain in a population with a low prevalence of vitamin D deficiency. It is plausible that treating deficiency would have benefit for pain, but these findings suggest that population-level supplementation in settings where the prevalence of vitamin D deficiency is low is not warranted.