Vitamin D and Nearsightedness
Friday, March 17, 2017
Study data collected by the Vitamin D Council and published by Springer Nature strongly suggests that low vitamin D status is related to axiel length structure / function and an alarming increased risk of nearsightedness (also called myopia) developing in early childhood, adolescence and teenage years.
Part of this data was collected by researchers at the Catholic University of Korea in Seoul, South Korea, using research from the Korea National Health and Nutrition Examination Survey (KNHANES), an ongoing population-wide survey.
They examined vitamin D levels in 2,038 people ages 13 to 18 years and noted whether they had nearsightedness or not.
Based on this and other data, the Vitamin D Council now reports the prevalence of nearsightedness has increased significantly over recent years, affecting about 50 percent of young adults of European descent and up to 96 percent of South Koreans.
Additionally, more children are now developing nearsightedness at an earlier age, with anywhere between 2 and 13 percent of the population being diagnosed by the age of six years, depending on the region.
Previous research has shown that time spent outdoors may decrease the risk of developing nearsightedness.
It is hypothesized by the Vitamin D Council and other esteemed scientists that this may be due to increased dopamine in the retina upon exposure to light or the vitamin D production that takes place when the skin is exposed to the sun. However, it remains unclear whether it's vitamin D or another product of sun exposure that is responsible for this protective effect.
The major circulating form of vitamin D is 25-hydroxyvitamin D, referred to as 25(OH)D in lab tests and clinical studies.
Dutch researchers recently investigated the relationship between vitamin D status, axial length and risk of nearsightedness in six- year-old children. They also looked at the effect of time spent outdoors on these factors.
A total of 2,665 children who participated in their Generation R birth-cohort study were included. The researchers evaluated the participants visual acuity and axial length, measured their serum 25(OH)D levels and gathered information regarding the participants' outdoor exposure via questionnaire.
Here is what the researchers determined:
- The 25(OH)D concentration of the participants averaged 27.5 ng/ml (68.8 nmol/l).
- A total of 2.3 percent of the children were diagnosed with nearsightedness.
- Only 18 percent of the children with nearsightedness had vitamin D levels ≥ 30 ng/ml (75 nmol/l).
- Serum 25(OH)D levels were inversely related to axial length for all individuals (p < 0.001). This relationship remained significant even after excluding nearsighted children (p < 0.02).
- After adjusting for confounding factors, including time spent outdoors, the relationship between vitamin D status and axial length remained significant (p < 0.01).
- Participants experienced a 35 percent decreased odds of nearsightedness per each 10 ng/ml increase in 25(OH)D status.
The researchers concluded: “In this cohort study of young children, we found a significant association between serum 25(OH)D levels, axial length and nearsightedness. This effect appeared independent of outdoor exposure and may suggest a more direct role for 25(OH)D in nearsighted pathogenesis.
As always, the researchers stress how important it is to note both the strengths and weaknesses of the study. The large size, use of multiple measurements of nearsightedness and the adjustment for several potential confounders increased the validity of this study. However, the young age of the participants decreased the number of cases of elongated axial length and / or nearsightednessdue to the lack of excessive eye growth, which typically starts appearing in adolescents. Also, the design of the study only showed correlation, not causality.
The Dutch researchers call for additional longitudinal and clinical trials to provide a further understanding of the relationship between vitamin D, sun exposure and nearsightedness.
Ellen Troyer, with Spencer Thornton, MD, and the Biosyntrx staff
The following statement from the American Academy of Ophthalmology, "Nearsightedness (also referred to as myopia) is a refractive error, which means that the eye does not bend or refract light properly to a single focus to see images clearly. In nearsightedness, close objects look clear but distant objects appear blurred. Nearsightedness is a common condition that affects a growing percentage of Americans. It is an eye focusing disorder, not an eye disease."
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