Vitamin D for vegans

Vitamin D is an essential nutrient which plays a critical role in the absorption and regulation of calcium and phosphorus, the building blocks for bones and muscles [1]. Without vitamin D, the reduced intestinal ability to absorb these minerals from foods can affect bone and muscle health. Besides, vitamin D also plays a critical role in many other body functions, such as the immune system [2], inflammatory regulation [3], blood glucose control [4],  blood clot prevention [5], and many more. No doubt, maintaining a sufficient level of vitamin D in the body is necessary for good health. The daily recommended allowance of vitamin D is 2.5µg for adults, whereas young children and pregnant and lactating mothers will require at least 10µg of intake [6].

Vitamin D is required for strong bones and muscles.

Vitamin D is unique among all other vitamins as it can be made in the skin through exposure to sunlight. For this reason, vitamin D is often called the ‘sunshine’ vitamin. Vitamin D exists in two common forms. The most natural form is vitamin D3 (cholecalciferol) which is synthesised in the skin by the reaction of 7-dehydrocholesterol with ultraviolet (UV)-B radiation that present in sunlight with a UV index of three or more. Vitamin D2 (ergocalciferol) is the other common form which is produced by some plants and fungi after stimulation with UV [6]. Vitamin D is classified as a fat-soluble vitamin alongside vitamins A, E and K as it is better dissolved in oil than water and stored in fat-tissue [7]. Not surprisingly, oily fish, including salmon, trout, mackerel, and sardines are listed among the best sources of vitamin D on the food chart, along with meat, milk and egg [8].

Sunlight is the necessary ingredient for the synthesis of vitamin D.

Vitamin D deficiency

Vitamin D deficiency is a common health issue. Even in sunny tropical Singapore, a cross-sectional study of 114 healthy adults found 42% of them to be vitamin D deficient (< 20 ng/mL) [9]. Common risk factors for Vitamin D deficiency are [10]:

  • old age
  • darker skin pigmentation
  • working indoor
  • habitually wearing long-sleeved, protective clothing, or stays in the shade
  • exclusively breastfed infants
  • low calcium intake
  • obesity
  • immobility
  • reduced kidney function or with chronic kidney disease
  • malabsorption syndrome
  • taking medication that has interactions or decreases absorption with vitamin D
Elderly people who stay indoors most of the time have a higher risk of vitamin D deficiency.

As vegetarians do not consume fish and meat and vegans will exclude even milk and egg, it is generally thought that such diet restrictions will increase the risk of vitamin D deficiency. However, it is not necessarily the case. A study among the Seventh-day Adventists with a diverse cohort ranging from vegans to meat-eaters found that the level of vitamin D status in the body, measured by serum 25-hydroxyvitamin D (25-OH D), was not associated with vegetarian status. Instead, factors such as vitamin D supplementation, degree of skin pigmentation, and the amount and intensity of sun exposure have a greater influence on the 25-OH D level than diet [11]. While some studies showed vegans and vegetarians had a lower level of 25-OH D level than meat-eaters, factors such as the amount of sunshine exposure and lifestyles are also prominent determinants [12,13].

It is possible to maintain an optimal level of vitamin D level as a vegan.

Hence, it is possible to maintain an optimal level of vitamin D level in the body with a plant-based diet.  Below are some recommendations.

Spend time outdoors

Spending time outdoors with activities such as exercising or gardening can increase the chance of sunlight exposure and reduce the likelihood of low vitamin D status [14]. It is recommended to have exposure to sunlight about 10-30 minutes a day, several times a week. Also, remember to have your arms and legs uncovered to receive sun exposure. If you spend an extended period outdoors, then remember to put on some sunscreen for protection from UV-A, which can be harmful to the skin, and reduce the chance of UV-A radiation-induced damage.

The best time for sun exposure is the middle of the day, rather than in the afternoon or morning.

While it was previously suggested that the public should avoid the hot sun at noon, recent research based on the ratio of UV-A to UV-B, found the contrary. The best time for sun exposure is the middle of the day, rather than in the afternoon or morning because the optimal UV-B: UV-A ratio is maximal at noon [15]. Therefore, walking outdoor under the sun during lunch break is a good way for those who work indoor to get their daily dose of vitamin D.

Plant-based vitamin D foods

Vitamin D2 is the primary form found in plant-based foods. One good source is mushroom, especially dried mushroom or UV-B-exposed fresh mushroom. A study that examined 35 types of dried mushrooms from China found that they contain 16.88 µg/g of vitamin D2 on average. Furthermore, these dried mushrooms also had an average vitamin B2 content of 12.68 µg/g [16]. Hence, fungus, especially the sundried version, should be a part of any vegan diet. Another potential source of vitamin D is seaweeds. Fresh kombu or kelp contains a low amount of vitamin D3 that can be increased with the sun drying process [17].

Make sure to add mushrooms and seaweeds to your vegan diet!

Fortification is done as part of the public health strategy to enhance nutrient intakes in the population. Fortified food products such as breakfast cereals, non-dairy milk, orange juice, or bread are more stable sources of vitamin D in a vegan diet. These are plant-based food products with additional vitamin D added. The use of these foods have been shown to improve vitamin D status and is considered safe [18].

Vitamin D supplementation

Taking vitamin D supplements is a good way of boosting vitamin D level. The common dosage is at 1000IU/day [19,20]. However, a higher dosage of 2000-3000IU/day may be needed to restore a deficiency state [21]. However, too much vitamin D can be toxic to the body. Therefore, taking a higher dosage of vitamin D supplements should only be done under the advice and supervision of a health practitioner. It is not recommended to take vitamin D supplements beyond 4000IU/day [22]. When considering vitamin D supplements, beware that not all of them are suitable for vegan. While vitamin D2 is plant-based and always safe to use, vitamin D3 can come from animal sources. Do check the product information to make sure that the product is vegan friendly.

Conclusion

Vitamin D deficiency is common due to aging and reduced exposure to sunlight in modern lifestyles. Vegans are not particularly at risk of such deficiency. Spending time outdoors, including mushrooms, seaweeds, and fortified food products in the diet, and periodically taking vitamin D supplement are ways to maintain an optimal level of vitamin D.

References

[1]        H.F. DeLuca, The control of calcium and phosphorus metabolism by the vitamin D endocrine system., Ann. N. Y. Acad. Sci. 355 (1980) 1–17. doi:10.1111/j.1749-6632.1980.tb21323.x.

[2]        C. Aranow, Vitamin D and the immune system, J. Investig. Med. 59 (2011) 881–886. doi:10.2310/JIM.0b013e31821b8755.

[3]        W. Liu, L. Zhang, H.-J. Xu, Y. Li, C.-M. Hu, J.-Y. Yang, M.-Y. Sun, The anti-inflammatory effects of vitamin D in tumorigenesis, Int. J. Mol. Sci. 19 (2018) 2736. doi:10.3390/ijms19092736.

[4]        I. Kostoglou-Athanassiou, P. Athanassiou, A. Gkountouvas, P. Kaldrymides, Vitamin D and glycemic control in diabetes mellitus type 2, Ther. Adv. Endocrinol. Metab. 4 (2013) 122–128. doi:10.1177/2042018813501189.

[5]        K. Khademvatani, M.H. Seyyed-Mohammadzad, M. Akbari, Y. Rezaei, R. Eskandari, A. Rostamzadeh, The relationship between vitamin D status and idiopathic lower-extremity deep vein thrombosis, Int. J. Gen. Med. 7 (2014) 303–309. doi:10.2147/IJGM.S64812.

[6]        A.M. Chandra, Vitamin D: Recommended dietary allowances, food sources, and side effects, HealthXchange.Sg. (n.d.). https://www.healthxchange.sg/food-nutrition/supplements/vitamin-d-recommended-dietary-allowances-food-sources-side-effects (accessed July 27, 2020).

[7]        A.A. Albahrani, R.F. Greaves, Fat-soluble vitamins: Clinical indications and current challenges for chromatographic measurement, Clin. Biochem. Rev. 37 (2016) 27–47. https://pubmed.ncbi.nlm.nih.gov/27057076.

[8]        U.S. Department of Health and Human Services and U.S. Department of Agriculture, 2015–2020 Dietary Guidelines for Americans, 8th ed., 2015. http://health.gov/dietaryguidelines/2015/guidelines/

[9]        X. Bi, S.L. Tey, C. Leong, R. Quek, C.J. Henry, Prevalence of vitamin D deficiency in Singapore: Its implications to cardiovascular risk factors, PLoS One. 11 (2016) e0147616–e0147616. doi:10.1371/journal.pone.0147616.

[10]      L.U. Gani, C.H. How, Vitamin D deficiency, Singapore Med. J. 56 (2015) 433–437. doi:10.11622/smedj.2015119.

[11]      J. Chan, K. Jaceldo-Siegl, G.E. Fraser, Serum 25-hydroxyvitamin D status of vegetarians, partial vegetarians, and nonvegetarians: the Adventist Health Study-2, Am. J. Clin. Nutr. 89 (2009) 1686S-1692S. doi:10.3945/ajcn.2009.26736X.

[12]      F.L. Crowe, M. Steur, N.E. Allen, P.N. Appleby, R.C. Travis, T.J. Key, Plasma concentrations of 25-hydroxyvitamin D in meat eaters, fish eaters,  vegetarians and vegans: results from the EPIC-Oxford study., Public Health Nutr. 14 (2011) 340–346. doi:10.1017/S1368980010002454.

[13]      J.A. Baig, S.A. Sheikh, I. Islam, M. Kumar, Vitamin D status among vegetarians and non-vegetarians., J. Ayub Med. Coll. Abbottabad. 25 (2013) 152–155.

[14]      M. De Rui, E.D. Toffanello, N. Veronese, S. Zambon, F. Bolzetta, L. Sartori, E. Musacchio, M.C. Corti, G. Baggio, G. Crepaldi, E. Perissinotto, E. Manzato, G. Sergi, Vitamin D deficiency and leisure time activities in the elderly: are all pastimes the same?, PLoS One. 9 (2014) e94805–e94805. doi:10.1371/journal.pone.0094805.

[15]      M. Grigalavicius, J. Moan, A. Dahlback, A. Juzeniene, Daily, seasonal, and latitudinal variations in solar ultraviolet A and B radiation  in relation to vitamin D production and risk for skin cancer., Int. J. Dermatol. 55 (2016) e23-8. doi:10.1111/ijd.13065.

[16]      G. Huang, W. Cai, B. Xu, Vitamin D2, ergosterol, and vitamin B2 Content in commercially dried mushrooms marketed in china and increased vitamin D2 content following UV-C irradiation, Int. J. Vitam. Nutr. Res. 87 (2016) 1–10. doi:10.1024/0300-9831/a000294.

[17]      L.J. Hughes, L.J. Black, J.L. Sherriff, E. Dunlop, N. Strobel, R.M. Lucas, J.F. Bornman, Vitamin D content of Australian native food plants and Australian-grown edible seaweed, Nutrients. 10 (2018). doi:10.3390/nu10070876.

[18]      L. O’Mahony, M. Stepien, M.J. Gibney, A.P. Nugent, L. Brennan, The potential role of vitamin D enhanced foods in improving vitamin D status, Nutrients. 3 (2011) 1023–1041. doi:10.3390/nu3121023.

[19]      S. Pilz, A. Zittermann, C. Trummer, V. Theiler-Schwetz, E. Lerchbaum, M.H. Keppel, M.R. Grübler, W. März, M. Pandis, Vitamin D testing and treatment: a narrative review of current evidence, Endocr. Connect. 8 (2019) R27–R43. doi:10.1530/EC-18-0432.

[20]      M.R. Rooney, L. Harnack, E.D. Michos, R.P. Ogilvie, C.T. Sempos, P.L. Lutsey, Trends in Use of High-Dose Vitamin D Supplements Exceeding 1000 or 4000 International Units Daily, 1999-2014, JAMA. 317 (2017) 2448–2450. doi:10.1001/jama.2017.4392.

[21]      P.J. Veugelers, T.-M. Pham, J.P. Ekwaru, Optimal Vitamin D Supplementation Doses that Minimize the Risk for Both Low and High Serum 25-Hydroxyvitamin D Concentrations in the General Population, Nutrients. 7 (2015) 10189–10208. doi:10.3390/nu7125527.

[22]      E. Marcinowska-Suchowierska, M. Kupisz-Urbańska, J. Łukaszkiewicz, P. Płudowski, G. Jones, Vitamin D toxicity – A clinical perspective, Front. Endocrinol. (Lausanne). 9 (2018) 550. doi:10.3389/fendo.2018.00550.

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