The idea that a vitamin D deficiency contributes to the risk of developing multiple sclerosis (MS) has been challenged in a recent study that examined subtle differences in a protein involved in vitamin D metabolism in people from different ethnic backgrounds.
The study, “Vitamin D-Binding Protein Polymorphisms, 25-Hydroxyvitamin D, Sunshine and Multiple Sclerosis,” was published in the journal Nutrients.
Vitamin D is processed by the body before being used, and converted to 25-hydroxyvitamin D (25OHD) in the liver. Blood levels of 25OHD are used to monitor vitamin D levels in the lab.
Although exposure to ultraviolet (UV) radiation has been shown to be associated with a decreased risk of MS in whites, blacks, and Hispanics, an association between higher serum 25OHD and reduced risk of MS has only been observed in whites.
It has been suggested that this is because 25OHD is a poor indicator of vitamin D levels in blacks. One possible explanation could be that the main transporter for 25OHD, known as a vitamin D-binding protein (DBP), may be different in blacks and Hispanics than in whites, most likely due to different gene sequences known as polymorphisms.
To test this hypothesis, researchers analyzed individuals from the three ethnic groups — 514 whites (247 with MS and 267 healthy people in a control group), 380 Hispanics (183 MS/197 controls), and 247 blacks (116 MS/131 controls). Several parameters were analyzed, namely serum 25OHD levels, type of DBP polymorphisms, UV exposure data, and MS risk factors.
Researchers observed significant differences in the dominant form of DBP found in the three ethnic groups. However, these differences could not explain the lack of association between 25OHD levels and MS in blacks and Hispanics.
Data also showed that a high UV exposure was significantly associated with a lower risk of MS in all three ethnic groups.
“Racial/ethnic variations in bioavailable vitamin D do not explain the lack of association between 25OHD and MS in blacks and Hispanics. These findings further challenge the biological plausibility of vitamin D deficiency as causal for MS,” the researchers wrote.
The study highlights the importance of recognizing the complex interplay between genetic variation, environmental factors, and disease risks in general.