de Koning, E J 2020, ' Emotional and physical health in older persons: a role for vitamin D? ', Doctor of Philosophy, Vrije Universiteit Amsterdam . < http://hdl.handle.net/1871.1/e4cdc2b2-334b-4187-a956-3de6a0601872 > de Koning, E J 2020, ' Emotional and physical health in older persons: a role for vitamin D? ', PhD, Vrije Universiteit Amsterdam .