Chicken or the Egg: Vitamin D and a Healthy Liver
Harvard University educator, philosopher, psychologist, and physician William James pragmatically said, “Is life worth living? It all depends on the liver”. A century later this quote is taking on new meaning. Non-alcoholic fatty liver disease (NAFLD) is now the most common cause of chronic liver disease. WebMD reports that 20% of adults and more than 6 million children may have NAFLD. The incidence is higher in individuals who are obese or have diabetes.
Jablonski and colleagues used a retrospective cohort study design to examine records from 130,000 adults admitted to 23 hospitals and 150 outpatient clinics. They identified 607 patients with NAFLD with serum 25(OH)D measurements. They compared findings with 607 controls randomly selected from 62,757 adults in the database who did not have a NAFLD diagnosis.
Serum 25(OH)D levels were significantly lower in NAFLD patients (65 vs 73 nmol/L; average age of 55 y). The NAFLD patients had higher BMI (333 vs 30 kg m-2) and had diabetes (36 vs 26%), peripheral vascular disease (12 vs 7%), liver disease (16 vs 8 %), and elevated liver enzymes compared to controls. After adjusting for these variables in a regression analyses, low serum 25(OH)D levels were significantly related with an increased incidence of NAFLD. The association does not show causality but it demonstrates a relationship between vitamin D status and non-alcoholic fatty liver disease. It should also be noted that the study population had better vitamin D status than the average American. According to the CDC 2nd Nutrition Report Table 220.127.116.11, the average vitamin D status for adults 40-59 years is 56 nmol/L.
Lower serum 25(OH)D levels are found in people with signs of inflammation. The vitamin D receptor (VDR) and serum 25(OH)D levels have been previously linked to NAFLD (Barchetta et al, 2012). The liver is central to the metabolism of vitamin D. We still don’t know which comes first, the chicken or the egg, when it comes to the association of vitamin D status and non-alcoholic fatty liver disease.
As scientists unravel this mystery, it is prudent, and wise, to stack the odds in your favor by consuming the dietary reference intakes (DRIs) for adequacy: 400IU for infants 0-12 months, 600 IU for those 1 to 70y (including women who are pregnant and lactating), and 800IU daily for those >70 y.
Jablonski KL, Jovanovich A, Holmen J, Targher G, McFann K, Kendrick J, Chonchol M. Low 25-hydroxyvitamin D level is independently associated with non-alcoholic fatty liver disease. 2012 Nutr Metab Cardiovasc Dis doi:10.1016/j.numecd.2012.12.006
Journal of Nutrition June 2013 Supplement. http://www.cdc.gov/nutritionreport/pdf/J_Nutr_Supplement_Factsheet.pdf
Barchetta I, Carotti S, Labbadia G, Gentilucci UV, Silecchia G, Leonetti F, Fraiili A, Picardi A, Morini S, Cavallo MG. 2012 Hepatology doi:10.1002/hep.25930