The World Health Organization defines health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.” It is not enough to simply measure the biological effects of a certain treatment and intervention; quality of life needs to be assessed as well.
Patient reported outcomes, including the measure of health related quality of life (HRQL), have been used for over 40 years and provide a unique and important metric for clinicians and researchers. HRQL is a measurement of how an individual’s well-being is influenced by a disease, disability, or disorder.
Because vitamin D has a multitude of roles throughout the body and is needed daily, it is important to determine whether vitamin D supplementation has any effects on HRQL. Numerous studies have looked at vitamin D and quality of life, however these have all been observational and have only looked at the relationship between vitamin D status and HRQL at a single time point.
A team of researchers recently conducted the first systematic review to assess the effect of vitamin D supplementation on quality of life outcomes in both healthy populations and populations of individuals suffering from various diseases and disorders.
They searched Medline and Web of Science databases for studies that administered vitamin D supplementation in human participants and measured and recorded HRQL as an outcome. A total of 15 studies met this criteria, with 11 of them being RCTs or intervention studies that involved some aspect of randomization and treatment.
Most of the studies used some variant of the Short Form (36) Health Survey (SF-36). The SF-36 creates scores based on eight sections, including vitality, bodily pain, and general health perceptions. Higher scores indicates greater HRQL.
Eight of the studies reported data on short-term (less than or equal to 6 months duration) studies and 7 studies reported data on long-term (greater than 6 months). Only three studies were conducted in healthy populations free of disease.
Sample sizes ranged from 28 to 33,067 participants. Only one long-term study used high-dose supplementation (greater than or equal to 100,000 IU/month), whereas half of the short-term studies used high-dose supplementation and the other half used low-dose supplementation.
Most studies used vitamin D3 but some used vitamin D2 or activated vitamin D analogs. Doses ranged from 400 IU/day to a single dose of 300,000 IU. Total doses of vitamin D ranged from 109,800 IU to 1,512,800 IU during the entire course of study. Some studies measured baseline and final 25(OH)D levels and some did not.
All participants had vitamin D levels below 30 ng/ml.
Due to the differences in the studies, a meta-analysis could not be performed. Instead, they looked at each study individually and formed an overall assessment regarding the impact of vitamin D supplementation on HRQL in both the short-term and long-term.
Here is what their review discovered:
The research team concluded,
“Based on this review, current evidence suggests that supplementation has a modest effect on HRQL in diseased populations over the short-term (less than 6 months), but insignificant effect on HRQL in healthy populations and diseased populations using vitamin D long-term. However, vitamin D may provide differential HRQL responses depending on the population under investigation, analog and dosage of supplement, duration of the study, and subscale or instrument used.”
The most important limitation to this review is the lack of similarity between the studies that prevents a meta-analysis of the data. This would have allowed the researchers a better look at the effect of vitamin D on HRQL and they lamented that such an analysis was not possible.
More studies of higher quality are needed in this area of research, both in healthy and diseased populations. Future studies should only include vitamin D deficient subjects, use daily doses of at least 5,000 IU of vitamin D3, and measure baseline and final 25(OH)D levels.