Low vitamin D levels are connected to increased symptom severity, anxiety, and depression in people with fibromyalgia (FM), a recent study suggests.
Some preliminary data has suggested that hypovitaminosis D (low vitamin D levels) may be a risk factor for fibromyalgia. Some studies suggest an association between low vitamin D levels and chronic, nonspecific pain, and other studies suggest that taking vitamin D supplements can improve FM symptoms.
However, the prevalence of hypovitaminosis D in people with FM is largely unknown, and its effects on this population also are unclear.
“The objective of our prospective questionnaire study was to investigate the association between hypovitaminosis D and FM symptom severity,” the researchers wrote. “Additionally, we sought to investigate the association of hypovitaminosis D with other secondary outcomes including mood disorders, fatigue, and quality of life.”
To that end, 593 people with FM (90.6% female, 89.9% white, average age 46.9 years) had their vitamin D levels measured and completed a battery of questionnaires. These included the Revised Fibromyalgia Impact Questionnaire (FIQ-R, which measures FM symptom severity), the seven-item Generalized Anxiety Scale (GAD-7, which measures anxiety), and the Patient Health Questionnaire-9 (PHQ-9, which measures depression).
Of the 593 participants, 122 (20.57%) had hypovitaminosis D, defined as vitamin D levels at or below 25 ng/mL. The researchers compared those with hypovitaminosis D to those without.
The two groups were similar in terms of most demographic characteristics, though the hypovitaminosis D had significantly higher average body mass index (BMI, 32.64 vs. 29.64 kg/m2) and proportion of non-whites (15.57% vs. 8.70%).
The average FIQ-R score was significantly higher among those with hypovitaminosis D (62.79 vs. 57.85). This difference remained statistically significant after adjustment for demographic factors including age, sex, and BMI.
“Our study demonstrated that vitamin D deficiency may be a risk factor for worse FM symptom severity as determined by the FIQ-R total score,” the researchers wrote. They further noted that FIQ-R scores above 59 are typically considered “severe,” suggesting clinical relevance in these average differences between the groups — that is, severe or moderate disease symptoms, respectively.
Average scores on the GAD-7 and PHQ-9 also were significantly higher in the hypovitaminosis D group (9.50 vs. 8.16 and 13.08 vs. 11.91, respectively). Again, these differences remained statistically significant after adjustment for demographic factors.
Vitamin D levels themselves did not correlate significantly with FIQ-R, GAD-7, or PHQ-9 scores after adjustment for demographic factors. In other words, this study showed an association between unhealthily low vitamin D levels and the various above symptoms, but not between these symptoms and vitamin D levels overall.
Additionally, there were no statistically significant differences in terms of fatigue (measured with the Multidimensional Fatigue Inventory) or quality of life (measured with the 36-item Short Form Health Survey) between the groups with or without hypovitaminosis D.
“In the FM patient population, hypovitaminosis D is common and may be associated with worse fibromyalgia symptom severity, anxiety, and depression,” the researchers concluded.
Importantly, the data show only an association, not causality, meaning that the data demonstrate hypovitaminosis D and worse FM symptoms tend to co-occur, but one does not directly cause the other.
“Future studies should extend these results longitudinally to assess causality and investigate the effects of vitamin D supplementation on physical and psychosocial functioning in the FM patient population,” the researchers wrote.
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