What is vitamin D and how do we get it?
Vitamin D is actually a prohormone that is essential in our bodies for many physiological processes including calcium and phosphorous absorption and regulating mechanisms in the immune system (Dominguez, 2021). Vitamin D deficiency is prevalent worldwide. Deficiency has been linked to rickets, osteomalacia (soft bones), osteoporosis, cardiovascular health, cognitive function and psychiatric conditions, ms, metobolic function (malabsorption syndromes such as celiac disease), and cancer (Cesari, 2011).
The primary source of vitamin D is internal synthesis in the skin after exposure to sun light! So get outside and soak up the sun everyday (though remember that sunscreen limits vit D production). We can also get vitamin D from food, mainly from animal sources like meat and eggs yolks and synthetic fortification.
Pork is a good source of dietary vitamin D
Pork is in general a good source of dietary vit D with a lean chop (219 g) offering 88 IU or about 15% of of the recommended intake (USDA - FoodData Central). These values are from conventionally raised american pork.
The vitamin D levels of fatty meat like ground and sausage are much higher than lean cuts. With fat easily having ten times more vitamin D than lean meats. Pork cooked in pork fat have higher vit D concentrations (Neill, 2022). Cooking with lard naturally increase the vit D of your diet! And in case you were wondering about nutrient retention after cookings, studies show that standard cooking methods don't degrade vitamin D levels (Neill, 2022).
Can sun light increase vitamin D in meat?
In animals, like humans, vit D is synthesized in the skin after sun exposure. This is a concept that has started to gain interest in the farm research world. Researchers are investigating the concept of biofortification - naturally improving the nutrient density and bioavilibility of crops. And studies are exploring how to increase the vitamin D in pork meat.
A study done at the University of Wyoming showed that vit D in pork loin doubled after just 1 hour/day of exposure to sun for two weeks prior to butchering (Larson-Meyer, 2017)!
The majority of pork in the US comes from pigs raised indoors with zero exposure to sunlight. Standard pig feed is supplemented with synthetic vit D to prevent the pigs from developing health issues like rickets and heart failure. Most scientific studies are aimed at the commercial farming industry so have focused on using artificial UV light from indoor lamps to increase the vit D content of pork.
A study at the Agri-Food and Biosciences Institute in the UK (Neill, 2023) using indoor lamps showed that daily exposure to UV light significantly increased the vitamin D content in pork. Another informative observation from this study, was that the posture of the pigs (standing up or sitting down - these are pigs in confinement) had an impact on vitamin D level. Pigs that stood longer during the daily light exposure having higher levels of vit D!
Most researchers are concerned with commercial applications of biofortification for pigs in confinement. Pasture raised pigs have free access to graze, root, and roam under the sun all of their life! Our pigs lived outside for their entire life.
Based on these few studies (there are so many more), it isn't a stretch to say that pasture-raised pigs have much higher vit D that standard pork. So eat pork as a part of healthy diet to improve your vit D levels!
And remember that magnesium is essential for the metabolism of vitamin D.
For more reading there is an informative case study out of the UK by L. Kirsty Pourshahidi titled "Improving Vitamin D in the Food Supply Chain: Is the (Bio)fortification of Pork Meat a Feasible Solution?" https://www.cabidigitallibrary.org/doi/10.1079/fsncases.2023.0003
Sources
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Dominguez LJ, Farruggia M, Veronese N, Barbagallo M. Vitamin D Sources, Metabolism, and Deficiency: Available Compounds and Guidelines for Its Treatment. Metabolites. 2021 Apr 20;11(4):255. doi: 10.3390/metabo11040255. PMID: 33924215; PMCID: PMC8074587.
- Cesari M, Incalzi RA, Zamboni V, Pahor M. Vitamin D hormone: a multitude of actions potentially influencing the physical function decline in older persons. Geriatr Gerontol Int. 2011 Apr;11(2):133-42. doi: 10.1111/j.1447-0594.2010.00668.x. Epub 2010 Dec 6. PMID: 21134097; PMCID: PMC4384440.
- U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. fdc.nal.usda.gov
- H.R. Neill, C.I.R. Gill, E.J. McDonald, W.C. McRoberts, R. Loy, L.K. Pourshahidi, Impact of cooking on vitamin D3 and 25(OH)D3 content of pork products, Food Chemistry, Volume 397, 2022, 133839, ISSN 0308-8146, https://doi.org/10.1016/j.foodchem.2022.133839.
- Larson-Meyer DE, Ingold BC, Fensterseifer SR, Austin KJ, Wechsler PJ, Hollis BW, Makowski AJ, Alexander BM. Sun exposure in pigs increases the vitamin D nutritional quality of pork. PLoS One. 2017 Nov 14;12(11):e0187877. doi: 10.1371/journal.pone.0187877. PMID: 29136033; PMCID: PMC5685574.
- H.R. Neill, C.I.R. Gill, E.J. McDonald, R. McMurray, W.C. McRoberts, R. Loy, A. White, R. Little, R. Muns, E.J. Rosbotham, U. O'Neill, S. Smyth, L.K. Pourshahidi, Improving vitamin D content in pork meat by UVB biofortification, Meat Science, Volume 199, 2023, 109115, ISSN 0309-1740, https://doi.org/10.1016/j.meatsci.2023.109115.