Environmental factors, such as time spent outdoors and near work, are commonly thought to play a key role in myopia development. A team of researchers from the University of California at Berkeley School of Optometry also suggests that individuals with increased insulin levels may be at greater risk of the condition.

Their study, published in Optometry & Vision Science, also found gender and age seemed to be most closely tied to myopia and its severity, while nutritional factors including serum vitamin D, plasma glucose and caffeine intake, didn’t appear to influence whether a person developed the condition.

In addition to older individuals, female participants were more likely to be myopic compared with males (38% vs. 33%), and women also comprised more of the acute myopia cases (-2.78D vs. -2.54D).

Using data from the National Health and Nutrition Examination Survey from 2003 to 2008, the investigators evaluated records of 6,855 ethnically diverse US residents aged 12 to 25. The study evaluated vision exam results, demographics, body metrics and nutritional markers and their potential association with myopia.

In addition to female sex and age, refractive error was the most significant factor related to myopia. In general, neither body metrics (BMI) nor nutritional factors (serum vitamin D, glucose levels and caffeine intake) were found to be associated with refractive error or myopia. However, increased insulin levels were linked to greater odds of developing myopia.

Because increased time spent outdoors is recognized as potentially being protective against myopia, there has been interest in whether vitamin D alone might be preventative, yet this association has been inconclusive in the literature. In the current study, African American individuals had the lowest serum levels of vitamin D, yet this group had the lowest number of myopes (35%, 1% below the average).

Since nutritional and body metrics didn’t appear to be closely associated with the presence or magnitude of myopia, these largely negative findings suggest that other environmental factors, such as those related to the visual environment, may contribute more to the development and/or progression of myopia, the authors said.

Continued research in these areas is needed to support more evidence-based myopia clinical management, they added.