Cognitive and neural correlates of vitamin D deficiency : focus on healthy aging and Alzheimer's disease

Vitamin D deficiency is a global public health concern due to its influence on health and well-being in which individuals have less than the minimum required concentration of vitamin D in their body and brain. Holick and Chen (2008) have estimated that 1 billion individuals worldwide have vitamin D deficiency. Although the definitive levels of vitamin D have not been agreed upon worldwide, Pettersen (2016) defined levels of vitamin D as follows: insufficient as being levels less than 50 nmol/L, low sufficient being between 50 and 75 nmol/L, high sufficient being between 75 and 100 nmol/L, and supratherapeutic being equal to or more than 100 nmol/L (Pettersen, 2016, p. 467).