Here are the references: Foundational
Asif T, Mohiuddin A, Hasan B, Pauly RR. Importance of Thorough Physical Examination: A Lost Art. Cureus. 2017;9(5):e1212.
Newton C. The Functional Nutrition-Focused Physical Exam. IFNA Track 3 Module 2.
Tongue
Jeghers H. Nutrition: the appearance of the tongue as an index of nutritional deficiency. New England Journal of Medicine. 1942;227:221-8.
Khayamzadeh M, Najafi S, Sadrolodabaei P, Vakili F, Kharrazi Fard MJ. Determining salivary and serum levels of iron, zinc and vitamin B12 in patients with geographic tongue. J Dent Res Dent Clin Dent Prospects. 2019;13(3):221-226.
Chiang CP, Chang JY, Wang YP, Wu YH, Wu YC, Sun A. Atrophic glossitis: Etiology, serum autoantibodies, anemia, hematinic deficiencies, hyperhomocysteinemia, and management. J Formos Med Assoc. 2020;119(4):774-780.
Skin
Salem I, Ramser A, Isham N, Ghannoum MA. The Gut Microbiome as a Major Regulator of the Gut-Skin Axis. Front Microbiol. 2018;9:1459.
Wang X, Li Y, Wu L, et al. Dysregulation of the gut-brain-skin axis and key overlapping inflammatory and immune mechanisms of psoriasis and depression. Biomed Pharmacother. 2021;137:111065.
Jafferany M, Franca K. Psychodermatology: Basics Concepts. Acta Derm Venereol. 2016;96(217):35-7.
Reunala T, Salmi TT, Hervonen K, Kaukinen K, Collin P. Dermatitis Herpetiformis: A Common Extraintestinal Manifestation of Coeliac Disease. Nutrients. 2018;10(5):602.
Stefanadi EC, Dimitrakakis G, Antoniou CK, et al. Metabolic syndrome and the skin: a more than superficial association. Diabetol Metab Syndr. 2018;10:9.
Hair
O'Connor K, Goldberg LJ. Nutrition and hair. Clin Dermatol. 2021;39(5):809-818.
Arck PC, Overall R, Spatz K, et al. Towards a "free radical theory of graying": melanocyte apoptosis in the aging human hair follicle is an indicator of oxidative stress induced tissue damage. FASEB J. 2006;20(9):1567-9.
Zhang B, Ma S, Rachmin I, et al. Hyperactivation of sympathetic nerves drives depletion of melanocyte stem cells. Nature. 2020;577(7792):676-681.
Poonia K, Bhalla M. Premature Graying of Hair: A Comprehensive Review and Recent Insights. Indian Dermatol Online J. 2024;15(5):721-731.
Nails
Singal A, Arora R. Nail as a window of systemic diseases. Indian Dermatol Online J. 2015;6(2):67-74.
Cashman MW, Sloan SB. Nutrition and nail disease. Clin Dermatol. 2010;28(4):420-5.
Eyes
Knapp A. The Eye as a Guide to Latent Nutritional Deficiency Diseases. Bull N Y Acad Med. 1946.
Wakamatsu TH, Dogru M, Tsubota K. Tearful relations: oxidative stress, inflammation and eye diseases. Arq Bras Oftalmol. 2008;71(6 Suppl):72-9.
Seydou A, Arnould L, Gabrielle PH, et al. Plasma Fatty Acids Pattern and Dry Eye Disease in the Elderly: The Montrachet Population-Based Study. Nutrients. 2022;14(11):2290.
Bu Y, Shih KC, Tong L. The ocular surface and diabetes, the other 21st Century epidemic. Exp Eye Res. 2022;220:109099.
Rahman A, Yahya K, Ahmed T, Sharif-Ul-Hasan K. Diagnostic value of tear films tests in type 2 diabetes. J Pak Med Assoc. 2007;57(12):577-81.
Seifart U, Strempel I. Trockenes Auge und Diabetes mellitus [The dry eye and diabetes mellitus]. Ophthalmologe. 1994;91(2):235-9.
Campagnoli LIM, Varesi A, Barbieri A, Marchesi N, Pascale A. Targeting the Gut-Eye Axis: An Emerging Strategy to Face Ocular Diseases. Int J Mol Sci. 2023;24(17):13338.