(1) Lehmann, U., Hirche, F., Stangl, G.I., Hinz, K., Westphal, S. & Dierkes, J. (2013) Bioavailability of vitamin D2 and D3 in healthy volunteers, a randomized placebo-controlled trial. Journal of Clinical Endocrinology and Metabolism, 98 (11), pp.4339–4345.

(2) Christakos, S., Dhawan, P., Porta, A., Mady, L.J. & Seth, T. (2011) Vitamin D and intestinal calcium absorption. Molecular and Cellular Endocrinology, 347 (1–2), pp.25–29.

(3) Christakos, S., Lieben, L., Masuyama, R. & Carmeliet, G. (2014) Vitamin D endocrine system and the intestine. BoneKEy Reports, 3, p.496.

(4) Hewison, M. (2012) An update on vitamin D and human immunity. Clinical Endocrinology, 76 (3), pp.315–325

(5) Gubatan, J., Chou, N.D., Nielsen, O.H. & Moss, A.C. (2019) Systematic review with meta-analysis: association of vitamin D status with clinical outcomes in adult patients with inflammatory bowel disease. Alimentary Pharmacology and Therapeutics, 50 (11–12), pp.1146–1158.

(6) Jalili, M., Vahedi, H., Poustchi, H. & Hekmatdoost, A. (2019) Effects of Vitamin D supplementation in patients with irritable bowel syndrome: A randomized, double-blind, placebo-controlled clinical trial. International Journal of Preventive Medicine, 10 (1).

(7) Khayyat, Y. & Attar, S. (2015) Vitamin D deficiency in patients with irritable bowel syndrome: Does it exist? Oman Medical Journal, 30 (2), pp.115–118.

(8) Berridge, M.J. (2017) Vitamin D deficiency and diabetes. Biochemical Journal, 474 (8), pp.1321–1332.

(9) Pham, H., Rahman, A., Majidi, A., Waterhouse, M. & Neale, R.E. (2019) Acute respiratory tract infection and 25-hydroxyvitamin D concentration: A systematic review and meta-analysis. International Journal of Environmental Research and Public Health, 16 (17).

(10) Kaufman, H.W., Niles, J.K., Kroll, M.H., Bi, C. & Holick, M.F. (2020) SARS-CoV-2 positivity rates associated with circulating 25-hydroxyvitamin D levels S. V. Reddy ed. PLOS ONE, 15 (9), p.e0239252.

(11) Zittermann, A., Frisch, S., Berthold, H.K., Götting, C., Kuhn, J., Kleesiek, K., Stehle, P., Koertke, H. & Koerfer, R. (2009) Vitamin D supplementation enhances the beneficial effects of weight loss on cardiovascular disease risk markers. American Journal of Clinical Nutrition, 89 (5), pp.1321–1327.

(12) Janssen, C.E., Globig, A.M., Busse Grawitz, A., Bettinger, D. & Hasselblatt, P. (2019) Seasonal variability of vitamin D status in patients with inflammatory bowel disease – A retrospective cohort study M. Zmijewski ed. PLOS ONE, 14 (5), p.e0217238.

(13) Webb, A.R., Kazantzidis, A., Kift, R.C., Farrar, M.D., Wilkinson, J. & Rhodes, L.E. (2018) Meeting vitamin D requirements in white caucasians at UK latitudes: Providing a choice. Nutrients, 10 (4).

(14) NHS.UK 2020 Vitamin D [Online] Available at: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/ [Accessed 22/1/2021].

(15) EFSA. Europa.EU, 2016 Vitamin D: EFSA sets dietary reference values. Available at: https://www.efsa.europa.eu/en/efsajournal/pub/4547 [Accessed 21/1/2021].

(16) National Institutes of Health, 2020 Vitamin D [Online]. Available at: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ [Accessed: 22/1/2021].

(17) RNHRD.NHS.UK Vitamin D Deficiency [Online]. Available at: https://www.rnhrd.nhs.uk/uploads/files/444/Vit%20d%20info%20for%20min%20website%20Dr%20A.pdf. [Accessed:22/1/2021].

(18) Maresz, K. (2015) Proper calcium use: Vitamin K2 as a promoter of bone and cardiovascular health. Integrative Medicine (Boulder), 14 (1), pp.34–39.

(19) Nair, S. (2010) Vitamin D deficiency and liver disease. Gastroenterology and Hepatology, 6 (8), pp.491–493.

(20) Al-Badr, W. & Martin, K.J. (2008) Vitamin D and kidney disease. Clinical Journal of the American Society of Nephrology, 3 (5), pp.1555–1560.

(21) Young, M.R.I. & Xiong, Y. (2018) Influence of vitamin D on cancer risk and treatment: Why the variability? Trends in cancer research, 13, pp.43–53.

(22) Tabatabaeizadeh, S.-A., Tafazoli, N., Ferns, G., Avan, A. & Ghayour-Mobarhan, M. (2018) Vitamin D, the gut microbiome and inflammatory bowel disease. Journal of Research in Medical Sciences, 23 (1), p.75.

(23) Konstantynowicz, J., Elli, F.M., Sokolovic, S., Kuryaninova, V., Zakharova, I., Klimov, L., Nikitina, I., Malyavskaya, S., Dolbnya, S., Kasyanova, A., Atanesyan, R., Stoyan, M., Todieva, A., Kostrova, G. & Lebedev, A. (2019) Vitamin D Insufficiency in Overweight and Obese Children and Adolescents. Frontiers in Endocrinology | www.frontiersin.org, 1, p.103.

(24) Neale, R.E., Khan, S.R., Lucas, R.M., Waterhouse, M., Whiteman, D.C. & Olsen, C.M. (2019) The effect of sunscreen on vitamin D: a review. British Journal of Dermatology, 181 (5), pp.907–915.

(25) NHS.UK, 2018 How to get Vitamin D from Sunlight [Online]. Available at:  https://www.nhs.uk/live-well/healthy-body/how-to-get-vitamin-d-from-sunlight/#:~:text=Your%20body%20can’t%20make,your%20risk%20of%20skin%20cancer. [Accessed 21/1/2021].

(26) Gallagher, J.C. (2013) Vitamin D and Aging. Endocrinol Metab Clin North Am, 42 (2), pp.319–332.

(27) Jayachandran, M., Xiao, J. & Xu, B. (2017) Molecular Sciences A Critical Review on Health Promoting Benefits of Edible Mushrooms through Gut Microbiota.