Scientists and organizations have different opinions of what is considered a deficiency of vitamin D. Vitamin D levels between 0-30 ng/mL are considered deficient according to the Vitamin D Council and the National Institutes of Health. The Endocrine Society believes that a level lower than 20 ng/mL is a deficiency. The Food and Nutrition Board considers 0-11 ng/mL as deficient.
Patients in this study, though, who experienced the much lower brain functioning after cardiac arrest had a vitamin D level of 7.9ng/mL, while good brain functioning was found in people with a level over 12.5 ng/mL, according to Medical News Today.