Tekin, C., and G. . Gunes. “Investigation of the Relationships Between Life Satisfaction, Optimism, Happiness and Blood Lipid, Vitamin-D Levels of Individuals Aged 55 and over”. Annals of Medical Research, vol. 29, no. 6, June 2022, pp. 585-94, https://www.annalsmedres.org/index.php/aomr/article/view/4127.