Can Fish Improve Your Vitamin D Status?
Vitamin D is notoriously difficult to get in the diet. Excluding fortified sources such as dairy, the major naturally occurring source of vitamin D is seafood. Swordfish, salmon, and tuna are excellent sources of vitamin D, with one serving of these fish containing anywhere from 39-142 %DV. Sadly, in the real world, we just don’t eat a lot of fish: Americans only eat half a serving of seafood per day on average. Vitamin D status is a reflection of vitamin D intake, so this begs the question: how does fish consumption affect not only vitamin D intake, but also vitamin D status?
Lehmann et al. published a meta-analysis of randomized controlled trials of fish intake and had measured vitamin D status. After combining the results of 9 studies with a total of 640 subjects, the authors found that fish consumption increased serum vitamin D status by an average of 4.4 nmol/L. The response depended upon the type of fish to a certain degree: consumption of lean fish increased serum vitamin D status by 1.9 nmol/L, whereas fatty fish consumption increased serum vitamin D status by 6.8 nmol/L. When the analysis was limited to just long term studies (roughly 6 months in duration), the average increase in serum vitamin D status was 8.3 nmol/L. Unfortunately, these are not dramatic increases in vitamin D status and according to the authors, would not be sufficient to increase serum vitamin D status to the optimal range (>50 nmol/L).
We routinely hear about the importance of meeting our needs for vitamin D. Case in point: vitamin D was once again recognized as a “Nutrient of Public Health Concern” by the 2015 Dietary Guidelines Advisory Committee (DGAC). But we know that more than 90% of Americans do not get enough Vitamin D from food alone. Even the DGAC recognized that meeting the requirement for vitamin D from diet alone is extremely difficult, and now Lehmann and colleagues have shown that the primary natural source of vitamin D – namely fish – is not sufficient to improve vitamin D status to optimal levels. While fish consumption should of course be encouraged (fish is also an excellent source of the omega-3 fatty acids EPA & DHA - nutrients sorely lacking in the American diet), we shouldn’t forget that we have a simple and effective tools to help address this problem: dietary supplements. While of course not a substitute for a great diet, dietary supplements are an effective way to decrease the prevalence of vitamin D inadequacy among Americans.
Lehmann U, Gjessing HR, Hirche F, et al. Efficacy of fish intake on vitamin D status: a meta-analysis of randomized controlled trials. Am J Clin Nutr 2015; epub ahead of print.
Fulgoni VL 3rd, Keast DR, Bailey RL, Dwyer J. Foods, fortificants, and supplements: where do Americans get their nutrients? J Nutr 2011; 141: 1857-1864.