Low Vitamin D Levels Linked to Chronic Pain in Women

Allison Gandey

August 18, 2008

August 18, 2008 — Women with low vitamin D levels have more chronic widespread pain, a new study has found. The modest findings do not support the use of vitamin D status as a key determinant for chronic pain, researchers suggest, but they do raise interesting questions about the possible influence of endocrine or immunological factors. The work is published online August 12 in the Annals of the Rheumatic Diseases.

Chronic widespread pain is thought to be a multifactorial condition. To date, the focus has been on psychosocial influences, note the study investigators, led by Kate Atherton, MD, from the University College London Institute of Child Health, in the United Kingdom. Although associations between chronic pain and general psychological distress, depression, somatization, and other factors have been consistently reported, translating these observations into management strategies has been fairly unsuccessful, they note.

Vitamin D deficiency has been suggested as a new modifiable risk factor for chronic pain. Vitamin D is a hormone precursor, which is obtained either through diet or skin synthesis. Using a nationwide population sample of white British adults, the researchers wanted to examine the link between vitamin D and chronic pain.

Women With Vitamin D Levels of 75 to 99 nmol/L Had Less Pain

"To our knowledge, this study is the largest population-based examination of the association between vitamin D status and chronic widespread pain to date," write the researchers. The work is also the first to consider related variations in lifestyle factors or to focus on white ethnic groups, they add.

The study included more than 9300 participants in England, Scotland, or Wales born during 1 week in March in 1958 who had completed a biomedical assessment at age 45 years. Of these, 6824 participants had data on 25-hydroxyvitamin D and pain.

Investigators found that chronic pain levels varied by 25-hydroxyvitamin D concentration in women, but not in men. "In our study, the lowest prevalence of chronic widespread pain was observed for women with 25-hydroxyvitamin D 75 to 99 nmol/L," Dr. Atherton and her team report. "This is intriguing given that 25-hydroxyvitamin D 75 nmol/L has been previously suggested as the cutoff point for optimal bone health."

Prevalence of Chronic Pain in Relation to Vitamin D Concentrations in Women

25-Hydroxyvitamin D (nmol/L) Women with Chronic Pain (%)
< 25 14.4
25 – 49 14.8
50 – 74 11.6
75 – 99 8.2
> 100 9.8



 

The investigators report there was an interaction between vitamin D concentration and sex in relation to chronic pain (interaction P = .006), which was not fully explained by differences in lifestyle or social factors (adjusted interaction P = .03).

The researchers point to a number of limitations of the work. They note the vitamin D status of participants was obtained during the study and may not represent the patient's status during the time that chronic pain developed, which may have been years earlier.

They also suggest that given the cross-sectional design of the study, it is not possible to establish whether suboptimal vitamin D status results in an increased risk for pain or whether changes in the behavior of subjects with pain result in reduced vitamin D concentrations.

"The lack of a stronger association between vitamin D and chronic pain in our general population sample may suggest that pain is primarily indicative of a severe vitamin D deficiency rather than a more gradual response to varying concentrations," the researchers write.

Dr. Atherton and her team report that it is unclear why an association between vitamin D and pain was observed in women but not in men. They suggest that since the women in the cohort are still mostly premenopausal, perhaps the influences of hormonal vitamin D on the regulation of estrogen activity may at least partly contribute to this sex difference.

"Nevertheless," they add, "given the observational nature of these data, we cannot exclude the possibility that our finding of an association between vitamin D status and chronic pain in women (or the lack of any association in men) is confounded by unmeasured factors.

"Follow-up studies are needed to evaluate whether higher vitamin D intake might have beneficial effects on [chronic widespread pain] risk," they conclude.

The researchers have disclosed no relevant financial relationships.

Ann Rheum Dis. Published online August 12, 2008. Abstract

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