Vitamin D is a prehormone of which has two major forms, D2 (or ergocalciferol) and D3 (or cholecalciferol). Classically, Vitamin D is obtained from sun exposure, food, and supplements. Just under the skin, UV light converts cholesterol to pre–Vitamin D which is absorbed into the blood steam, then travels to the liver then the kidney. In these organs it is hydroxylated each time to reach its active form Calcitriol (1,25-Dihydroxycholecalciferol). In the past, its major role is to increase the flow of calcium into the bloodstream, by promoting absorption of calcium and phosphorus from food in the intestines, and reabsorption of calcium in the kidneys enabling normal mineralization and remodeling of bone by osteoblasts and osteoclasts. In deficiency states, Rickets can occur, particularly in children. Rickets can be remedied by sunshine and, in the winter, cod liver oil.
But this sunshine vitamin does much more. It improves the function of the cardiovascular, immune, neurologic, and endocrine systems and independently extends life. But to get the best out of this molecule, it must be given in sufficient amounts such as a daily intake of at least 10,000 IU which is what one can naturally get from the sun in a fair skin individual clad in a bathing suit without sun blockers between 10:00 AM and 3:00 PM in Oklahoma in the summer, assuming the kidneys and liver are normally functioning. Of course the downside will be terrific sunburn with an increase risk of skin aging and cancer. The darker the skin by previous tanning or genetically, the less this essential substance is produced. So according to the above, most of us have a deficiency of this miracle hormone-like vitamin. This is particularly true in the elderly, Afro-Americans, living in northern latitudes in the winter most of whom have a real deficit of this molecule.
To assume that all of us have a D insufficiency and to take 10,000 IU, may be fine, but to be more accurate and to insure that we do take the correct dose and not reach toxic levels a blood test is advisable. A random serum 25-hydroxy-vitamin D level is a satisfactory way to determine the cumulative effect of sun and diet in our body. Ideal levels are between 50 and 100ng/L rather than the greater than 15 printed on the lab slip. Be sure that it is expressed in ng/L rather than in nanamoles. If given in ng/L to convert to nanomoles multiply by 2.5.
Using information from the National Health and Nutrition Examination Survey a group of researchers concluded that having low levels of vitamin D (<17.8 ng/ml) was independently associated with an increase in all-cause mortality in the general population. The study evaluated whether low serum vitamin D levels were associated with all-cause mortality, cancer, and cardiovascular disease (CVD) mortality among 13,331 diverse American adults who were 20 years or older. Vitamin D levels of these participants were collected over a 6-year period (from 1988 through 1994), and individuals were passively followed for mortality through the year 2000. Shortening of leukocyte telomeres is a marker of aging. Leukocyte telomere length predicts the development of aging-related disease, and length of these telomeres decreases with each cell division and with increased inflammation (more common in the elderly). Vitamin D can inhibit proinflammatory overeaction and slow the turnover of leukocytes, longer leukocyte telomere length is achieved by the body maintaining the optimal vitamin D concentration.
Lack of vitamin D synthesis is a possible explanation for high rates of influenza and other respiratory infection during winter. The National Jewish Hospital recently published a study showing that there is a decrease of asthmatic attacks in patients who took 10,000 IU of D daily. Vitamin D has been shown to increase the activity of natural killer cells, and enhance the phagocytic activity of macrophages. Active vitamin D hormone also increases the production of cathelicidin, an antimicrobial peptide that is produced in macrophages triggered by bacteria, viruses, and fungi. The fact that MS is more common in the higher latitudes suggests a link between Vitamin D and this disease. It is postulated that it is due to the immune-response suppression properties of Vitamin D. Early in 2010 another paper indicated that this vitamin decreases the incidence of cases and the exacerbations of Crohn's the well known auto-immune/infectious disease. D is necessary for differentiating between self and foreign proteins in a subgroup of individuals genetically predisposed to various auto-immune diseases.
Vitamin D may both prevent and decrease the aggressiveness of cancer. Vitamin D plays a role in a wide range of cellular mechanisms in the development of cancer. A 2006 study using data on over 4 million cancer patients from 13 different countries showed a marked increase in some cancer risks in countries with less sun. Vitamin D reduced an individual's colon cancer risk by 50%, and breast and ovarian cancer risks by 30%. Low levels of vitamin D in serum have been correlated with breast cancer disease progression and bone metastases. A 2006 study found that taking even the RDA of vitamin D (400 IU per day) cut the risk of pancreatic cancer by 43% in a sample of more than 120,000 people from two long-term health surveys. Also in male smokers a 3-fold increased risk for pancreatic cancer in the highest compared to lowest quintile of serum 25-hydroxyvitamin D concentration has been found. A randomized intervention study involving 1,200 women, published in June 2007, reports that vitamin D supplementation resulted in a 60% reduction in cancer incidence, during a four-year clinical trial, caused a 77% reduction for cancers diagnosed after the first year, therefore excluding those cancers more likely to have originated prior to the vitamin D intervention
A recent report from the National Health and Nutrition Examination Survey involving nearly 5,000 participants found that low levels of vitamin D were associated with an increased risk of peripheral artery disease. The incidence of this was 80% higher in participants with the lowest vitamin D levels (<17). Cholesterol levels were found to be reduced in gardeners in the UK during the summer months. Low levels of vitamin D are associated with an increase in high blood pressure.
There is a certain amount of evidence to suggest that dietary vitamin D may be carried by lipoprotein particles into and out of the cells of the artery wall and atherosclerotic plaque, where it may be converted to inactive form by monocyte-macrophages. Higher Vitamin D levels have been correlated with calcified plaques, but these are more stable than the “soft” non-calcified lesions.
I have found over 250 peer-reviewed articles verifying that Vitamin D lowers the incidence and severity of Diabetes. Also this vitamin, perhaps because of its interaction with Vitamin A, greatly ameliorates psoriasis. I advise 5,000 to 15,000 IU a day with or without food, although its absorption may be better with meals. Some docs recommend it in higher doses (50,000 to 100,000 IU) weekly or even monthly, but we were intended to get our Vitamin D daily from sunlight, so I advise daily consumption. The Upper Intake Level of vitamin D for children and adults is set at 50 micrograms/day (2,000 IU). There have been published cases of individuals who have mistakenly taken 50,000 IU daily for 2 months without undue toxicity and blood values of only 200 ng/L. Vitamin D overdose, however, can cause hypercalcemia which has these main symptoms: anorexia, nausea, and vomiting, frequently followed by polyuria, polydipsia, weakness, nervousness, pruritus, and ultimately, kidney damage which may be irreversible. In my nearly 50 years as a physician, I have never seen such a case, nor have any of my colleagues.