The relationship between plasma 25-hydroxyvitamin D concentration and nonalcoholic fatty liver disease (NAFLD) does not appear to be causal, challenging prior observational evidence that increasing the vitamin could reduce disease risk and/or severity, according to research findings published in the September issue of the Journal of Hepatology.
Non-alcoholic fatty liver disease (NAFLD) is the result of fat being deposited into the liver not due to excessive alcohol use. As many as 80% of obese subjects and patients with type 2 diabetes have non-alcoholic fatty liver disease, however, the underlying causes of this condition are still under investigation. Inadequate diagnostic tools, addressing patient compliance issues, and the lack of long-term controlled trials are all major shortcomings to addressing an individual’s risk.
In a recent cross-sectional study, researchers in the Division of Endocrinology, Diabetes and Metabolism at the University of Florida measured clinical data from 239 patients at hospitals in San Antonio, Texas and Gainesville, Florida. Using state-of-the-art diagnostic tools including magnetic resonance imaging and spectroscopy, researchers screened for factors associated with NAFLD, and then divided individuals into three groups according to vitamin D levels, (normal > 30 ng/m , insufficient 20-30 ng/ml, and deficient < 20 ng/ml).
After matching patients for BMI and total body fat, researchers observed no significant differences between vitamin D levels and any of the following outcome measures: insulin resistance, liver fat accumulation, total body fat, or severity of liver disease. Researchers also found no association between plasma vitamin D concentration and non-alcoholic steatohepatitis (NASH); a more serious form of liver disease.
“This is the first study, to our knowledge, measuring plasma vitamin D levels in patients undergoing an in-depth characterization of their metabolic/liver profile using gold-standard diagnostic techniques,” says Dr. Kenneth Cusi, M.D., F.A.C.P., F.A.C.E., division chief of endocrinology, diabetes and metabolism at the University of Florida and lead author on the study. “We believe that the current data puts to rest an issue that has been extensively debated.”
To help clarify potential relationships between vitamin D levels and type 2 diabetes mellitus, researchers also classified patients according to their diabetes status, with similar results. Despite lacking a causal relationship between vitamin D and T2DM, “there are existing guidelines from respected medical agencies that recommend healthy weight and healthy lifestyle management, including a healthy diet and physical activity, to prevent the onset of type 2 diabetes.” Cusi said.
“Further investigation may be warranted to assess causality and the long-term role of vitamin D replacement, as well as specific subpopulations such as patients with T2DM, to fully assess the role that vitamin D deficiency may play in the development of the condition,” according to researchers.
Cusi, et. al. Relationship of Vitamin D with Insulin Resistance and Disease Severity in Nonalcoholic Steatohepatitis. J Hepatol. 2014 Sep 4.