Vitamin D3, also called Cholecalciferol or Colecalciferol, is a fat-soluble vitamin necessary for the maintenance of a healthy body and helps your body absorb calcium and phosphorus. Your body can make vitamin D3 or Cholecalciferol when your skin is exposed to ultraviolet rays from the sun. Vitamin D3 or Cholecalciferol is also produced industrially for use in nootropic supplements, and to fortify foods. It can also be produced using ultraviolet irradiation of 7-dehydrocholesterol extracted from lanolin in sheep’s wool. Vitamin D3 is usually used to relieve people of vitamin D deficiency and associated diseases, including rickets. It is also widely used to improve memory and cognitive function along with a decrease in several markers of AD pathology.
Vitamin D3 or Cholecalciferol is used as a dietary supplement in people who do not get enough vitamin D in their diets to maintain adequate health. It is very important since it regulates the production of phosphorous and calcium in the body. Vitamin D3 is broken down by the body into a substance called calcitrol which actually has very important cancer fighting properties.
As a nootropic supplement, Vitamin D3 is vital for optimal cognitive health. It’s an integral part of neurotransmitter synthesis, gene expression, DNA maintenance and repair, and the forms of neuroplasticity needed for memory formation and retrieval. It appears to be a more reliable form of supplemental vitamin D, relative to D2, for increasing serum levels to an adequate range. The other health benefits of Vitamin D3 are:
- Relieves heart disease and Improves heart health 
- Reduces depression and improves mood 
- Improves learning, memory and cognitive function 
- Maintains calcium levels and makes strong bones 
- Helps people against cancer 
- Develops the growth and maintenance of neurons 
- Helps people who have dementia, Parkinson’s, MLS, epilepsy, and schizophrenia 
- Helps people who have Alzheimer’s Disease (AD) 
- Helps against autism 
Vitamin D3 influences our autoimmune system, heart health, relieves infectious disease, and supports optimal cognition. On the other hand, Vitamin D3 deficiency has been linked to some common diseases such as Alzheimer’s and Parkinson’s disease, asthma, autism, depression, cancer, and diabetes. People who take a daily calcium and vitamin D3 supplement may be able to lose more weight than subjects taking a placebo supplement. It also has an appetite-suppressing effect.
How it works
The active form of Vitamin D3 or Cholecalciferol, 1,25-dihydroxycholecalciferol (calcitriol) plays an important role in maintaining blood calcium and phosphorus levels and mineralization of bone. The activated form of Cholecalciferol binds to vitamin D3 receptors and modulates gene expression. This leads to an increase in serum calcium concentrations by increasing intestinal absorption of phosphorus and calcium, promoting distal renal tubular re-absorption of calcium and increasing osteoclastic resorption. 
- Neurotransmitters: Vitamin D3 with Omega-3’s is needed for serotonin synthesis, release and function. Regulating executive function, sensory gating, and social behavior. And Vitamin D3 is involved in the synthesis of GABA, glutamate and glutamine, and dopamine in the brain.
- Neuroprotective: Vitamin D3 protects against DNA damage through prevention of telomere shortening and inhibition of telomerase activity. And prevents oxidative damage to DNA.
- Mood: Vitamin D3 is involved in neuromodulation, regulation of neurotrophic factors, neuroprotection, neuroplasticity, and brain development. All in areas of the brain associated with depression. Supplementation could be an important part of treatment of depression.
There are clearly a number of ways in which vitamin D can affect brain development and function and these tend to underline a beneficial role for vitamin D against aging processes and neurodegenerative diseases that ultimately lead to cognitive decline.
Though Vitamin D3 is extremely important for good health, it has some side effects, but usually not at normal doses. And many people using this medication do not have serious side effects.
Only too much vitamin D can cause harmful high calcium levels such as nausea/vomiting, constipation, loss of appetite, increased thirst, increased urination, mental/mood changes, unusual tiredness. If you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing, etc, you are suggested to contact your doctor right away.
The recommended dosage for taking Vitamin D3 can be 600 to 2000 international units, orally, but maximum dosage should not exceed 4000 international units per day, unless your doctor tells you to do.
However, the dosage can be different for different health conditions, such as if you have osteoporosis and are over 50 years old, you should take 800 to 1000 IU (20 to 25 mcg) a day of vitamin D3 with calcium. So you are recommended to consult with your doctor to determine the perfect dosage for your condition.