Remember that when you read an article regarding blood levels of vitamin D, you are usually reading an article about sunlight: in the general population, the source of 90% of vitamin D is sunlight exposure.
A recent study on the relationship between cognitive impairment (thinking disorders) and vitamin D levels came to some very interesting conclusions. Dr. David Llewellyn, the lead researcher, stated the following: “Compared with those patients with sufficient levels of vitamin D, those participants who were very vitamin D deficient had a 6-fold higher risk for cognitive impairment, with a doubling of risk still for those who were considered deficient (≥25 to <50)"” Dr. Llewellyn also stated that "low levels of vitamin D are just genuinely bad for the brain."
Vitamin D research continues to amaze. The evidence mounts that vitamin D deficiency has a profound negative influence on the function of the brain. Previously, I wrote of the compelling evidence that autism is a vitamin D deficiency disease and also presented research indicative of a role of vitamin D in reducing depression, elevating mood and increasing happiness. I also came across a small study of 17 psychiatric patients. Of these patients, two were borderline deficient and 15 were deficient. Seven had such low levels that blood tests could not produce an accurate reading. Encouragingly, the researchers recommended that mental-health inpatients receive adequate exposure to sunlight.
In my book, I documented the critical importance of sunlight/vitamin D to the development and health of the brain:
1. Prenatal vitamin D deficiency in animals profoundly alters brain development. ] Dr. Darryl Eyles and his colleagues state, “rats born to vitamin D-deficient mothers had profound alterations in the brain at birth.” The cortex was longer but not wider, the lateral ventricles were enlarged, the cortex was proportionally thinner and there was more cell proliferation throughout the brain… Our findings would suggest that low maternal vitamin D(3) has important ramifications for the developing brain."
2. Rats born to vitamin D-deficient mothers also have permanently damaged brains into adulthood and exhibit hyperlocomotion (excessive movement from place to place) at the age of ten weeks. Could this relate to hyperactivity in our children? Such rats also show impairment in learning and memory skills.
3. People hospitalized for bipolar disorder, and who are exposed to sunlight daily, are able to leave the hospital almost four days earlier than those who are not exposed, and people hospitalized for seasonal affective disorder (SAD) also have shorter stays when they are placed in rooms on the sunny side of the hospital.
4. Two studies of mice with abnormal vitamin D receptors (VDR) in the brain found an increase in anxiety, aggression, poor grooming, maternal pup neglect and cannibalism.  Abnormal VDR cause a situation similar to vitamin D deficiency; the vitamin D that is available cannot properly stimulate the genes that prevent the anxiety, cannibalism, etc.
5. Another vital function of vitamin D is in inducing the production of nerve-growth factor (NGF), a protein that is essential for proper development of nerve cells in the brain and elsewhere.  It is obvious that if vitamin D is not present, nerve cells will simply not develop as they should in the central nervous system and brain, leading to the mental disorders we discuss here.
Can it be that the Powers of Darkness (the “sunscare” promoters) are partially responsible for the widespread depression, negativism, anxiety and psychological disorder that plague our society to a greater extent each year? Their efforts, coupled with modern indoor lifestyles, are leading to increases in a plethora of diseases, some of which are disorders of the brain. I believe it will be only a matter of time until vitamin D deficiency in pregnant women will be correlated to abnormally low IQ in the children they bear. In another blog, I have already discussed autism as a vitamin D deficiency disease, and there is an indication that women who conceive in the fall and winter tend to bear more dyslexic children, as well as children with other learning and reading disabilities.   The nervous system’s critical time to develop neural connections is in the first months after conception. If the pregnant woman is low in vitamin D during that time, it could affect the development of the fetal brain.Activated vitamin D is a potent hormone that is essential for proper brain development.
As a society and as parents, we cannot wait for more research before acting on the crying need for optimal vitamin D levels. Our mental and physical health, as well as that of our children, depends on regular, non-burning exposure sunlight, or other sources of vitamin D.
 Susan Jeffery, Low Vitamin D Levels Associated With Increased Risk for Cognitive Impairment Medscape Today, July 13,2010.
 Tiangga, E. et al. Psychiatric Bulletin 2008;32:390-93
 Eyles, D. et al. Vitamin D3 and brain development. Neuroscience 2003;118:641-53.
 McGrath, J. et al. Vitamin D3-implications for brain development. J Steroid Biochem Mol Biol 2004;89-90:557-60.
 Feron, F. et al. Developmental vitamin D3 deficiency alters the adult rat brain. Brain Res Bull. 2005 Mar 15;65(2):141-8.
 Burne, T. et al. Transient prenatal Vitamin D deficiency is associated with hyperlocomotion in adult rats. Behav Brain Res 2004;154:549-55.
 Benedetti, F. et al. Morning sunlight reduces length of hospitalization in bipolar depression. J Affect Disord 2001;62:221-23.
 Beauchemin, K. et al. sunny hospital rooms expedite recovery from severe and refractory depressions. J Affect Disord 1996;40:49-51.
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 Carlson, A. et al. Is vitamin D deficiency associated with peripheral neuropathy? The Endocrinologist 2007;17:319-25.
 Livingston, R. et al. Season of birth and neurodevelopmental disorders: summer birth is associated with dyslexia. J Am Acad Child Adolesc Psychiatry. 1993;32:612-6.
 Badian, N. Reading Disability in an Epidemiological Context: Incidence and Environmental Correlates. J Learn Disabil. 1984;17:129-36.
 Martin, R. Season of birth is related to child retention rates, achievement, and rate of diagnosis of specific LD. J Learn Disabil 2004;37:307-17