A recent study published in the International Journal of Rheumatic Diseases discovered that vitamin D deficiency is strongly associated with dry eye and its severity.
Dry eye is a common condition in which the eyes do not have adequate moisture. Symptoms of dry eye typically include discomfort, stinging, redness and fatigue in the eyes, along with blurred vision and sensitivity to light. The etiology of dry eye is complex, but research suggests that inflammatory factors play a key role.
Researchers recently hypothesized that vitamin D plays a role in dry eyes due to its anti-inflammatory properties. In addition, researchers have proposed that vitamin D may help prevent dry eyes by inducing cathelicidin, an anti-microbial protein that can be produced by cells in the eyes and heal eye wounds.
In order to test this hypothesis, researchers recently compared the prevalence and symptom severity of dry eyes between 50 vitamin D deficient (levels less than 20 ng/ml or 50 nmol/l) women and 48 vitamin D sufficient (levels greater than or equal to 20 ng/ml or 50 nmol/l) women. The researchers only included pre-menopausal women, since postmenopausal hormonal changes have been found to be associated with dry eye.
The researchers used three different tests to diagnose dry eyes: Schirmer’s test, tear break-up time test (TBUT) and ocular surface disease index (OSDI). They also evaluated the functional status, pain severity and fatigue severity of the women by using the Stanford Health Assessment Questionnaire (HAQ), Visual analogue scale-pain (VAS-pain) and the Fatigue severity scale (FSS), respectively.
Here is what the researchers found:
- The average vitamin D levels were 13.45 ng/ml (33.63 nmol/l) and 47.64 ng/ml (119 nmol/l) of vitamin D deficient women and vitamin D sufficient women, respectively.
- 52% of the vitamin D deficient women had dry eyes according to Schirmer’s test compared to only 4% of the controls (p = 0.001).
- 74% of the vitamin D deficient women had dry eyes according to TBUT scores compared to 12% of the controls (p = 0.001).
- 70% of the vitamin D deficient women had dry eyes according to OSDI compared to 19% of the controls (p = 0.003).
- VAS-pain, HAQ and FSS scores were higher in the vitamin D deficient group than the control group (p < 0.005), indicating that those considered vitamin D deficient experienced increased pain, fatigue and functional impairment of the eye.
The researchers summarized the findings of the study,
“To our knowledge, our study is the first to demonstrate the association between dry eye and clinical parameters of hypovitaminosis D such as fatigue, functional impairment and pain.”
They went on to state the implications of their study,
“We are of the opinion that vitamin D plays a protective role in the development of dry eye, probably by enhancing tear film parameters and reducing ocular surface inflammation…Vitamin D supplementation may be useful for dry eye symptoms, including ocular discomfort, soreness, redness, ocular fatigue, sensitivity to light and blurred vision.”
As always, it’s important to critically evaluate the study. The primary limitation was the small sample size. The sample population was limited to pre-menopausal women, which limits the study’s generalizability. In addition, the study followed a case-control design, meaning that it was not capable of proving causality. Therefore, larger clinical trials are warranted.
However, it seems possible that if you keep your vitamin D level around 50 ng/ml (125 nmol/L), it is much less likely you will be bothered by dry eye.
Citation of article
Tovey, A. & Cannell, J. New study suggests vitamin D deficiency is related to dry eye. The Vitamin D Council Blog & Newsletter, 2015.