Vitamin D

Extracted from : Linus Pauling Institute » Micronutrient Information Center


  • Vitamin D can be synthesized in the skin upon exposure to sunlight and is then metabolized in the liver and kidney to the metabolically active form called 1α,25-dihydroxyvitamin D. Through binding to the vitamin D receptor (VDR), 1α,25-dihydroxyvitamin D can regulate the expression of hundreds of genes involved in skeletal and other biological function.


  • Vitamin D is essential for maintenance of bone mineralization through the regulation of calcium and phosphorus homeostasis. Vitamin D also exhibits many non-skeletal effects, particularly on the immune, endocrine, and cardiovascular systems.


  • Vitamin D is important for normal bone development and maintenance. Severe vitamin D deficiency causes rickets in children and osteomalacia in adults.


  • Secondary hyperparathyroidism due to vitamin D insufficiency can increase bone breakdown and precipitate osteoporosis. Randomized clinical trials indicate that supplementation with at least 800 IU/day of vitamin D may reduce the risk of falls and fractures in older individuals.


  • Vitamin D can regulate cell differentiation and growth by binding to the vitamin D receptor found in most body cells. Observational studies have reported associations between low sun exposure, poor vitamin D status, and increased risk of developing colorectal and breast cancer.


  • Various observational studies have reported inverse associations between vitamin D status and the susceptibility or severity of autoimmune diseases, including type 1 diabetes mellitus, multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematosus.


  • Vitamin D insufficiency in pregnant women may be associated with several adverse effects for the mother and newborn.


  • Recent preliminary studies have shown that vitamin D supplementation may offer promising improvements in the management of atopic dermatitis (eczema) and Crohn’s disease.

Vitamin D is a fat-soluble vitamin that regulates calcium  (homeostasis) state of balance, and is vital for bone health. While it can also be obtained from dietary sources or supplements, vitamin D3 (cholecalciferol) is synthesized in the human skin from 7-dehydrocholesterol upon exposure to ultraviolet-B (UVB) radiation from sunlight (see the separate article on Vitamin D and Skin Health).

Vitamin D2 (ergocalciferol) is a vitamin D analog photosynthesized in plants, mushrooms, and yeasts; vitamin D2 is also sometimes used in vitamin D food fortification. When vitamin D3 in skin is inadequate due to insufficient exposure to UVB radiation, oral intake of vitamin D is necessary to meet vitamin D requirements.


In vitamin D deficiency, calcium absorption cannot be increased enough to satisfy the body’s calcium needs (4). Consequently, PTH production by the parathyroid glands is increased and calcium is mobilized from the skeleton to maintain normal calcium concentrations — a condition known as secondary hyperparathyroidism. Although it has long been known that severe vitamin D deficiency has serious consequences for bone health, research suggests that less obvious states of vitamin D deficiency are common and increase the risk of osteoporosis and various other health problems.

Vitamin D deficiency causes muscle weakness and pain in children and adults. Muscle pain and weakness were prominent symptoms of vitamin D deficiency in a study of Arab and Danish Muslim women living in Denmark (11).

In a cross-sectional study of 150 consecutive patients referred to a clinic in Minnesota for the evaluation of persistent, nonspecific musculoskeletal pain, 93% had serum 25-hydroxyvitamin D concentrations equal to or below 20 ng/mL, with a mean concentration of 12.1 ng/mL, which is indicative of vitamin D insufficiency (12).

Loss of muscle strength greatly contributes to increased risk of falling and bone fractures, especially in older people. In addition, long-term vitamin D insufficiency may be a contributing factor to osteoporosis in the elderly (see Osteoporosis).

Although adult bones are no longer growing, they are in a constant state of turnover, or “remodeling.” In adults with severe vitamin D deficiency, the collagenous bone matrix is preserved, but bone mineral is progressively lost, resulting in a softening of bones (osteomalacia), bone pain, and increased risk of osteoporosis (13).

Acute respiratory infections

More than 200 viruses are responsible for causing familiar infections of the upper respiratory tract (URT), known as the common cold, resulting in symptoms of nasal congestion and discharge, cough, sore throat, and sneezing (15). The analysis of cross-sectional data from 18,883 participants (ages 12 years and older) of the Third US National Health and Nutrition Examination Survey (NHANES III) reported an inverse relationship between serum 25-hydroxyvitamin D concentrations and recent (self-reported) URT infection (URTI). High levels of vitamin D3 are associated with lower chances of getting the common cold. A subgroup analysis indicated that low concentrations of serum 25-hydroxyvitamin D in subjects with asthma and chronic obstructive pulmonary disease (COPD) were linked to a greater susceptibility to URTI when compared to people without pulmonary disease.

Sources of Vitamin D

Solar ultraviolet-B radiation (UVB; wavelengths of 290 to 315 nanometers) stimulates the production of vitamin D3 in the epidermis of the skin (5). Sunlight exposure can provide most people with their entire vitamin D requirement. Children and young adults who spend a short time outside two or three times a week will generally synthesize all the vitamin D they need to prevent deficiency.

One study reported that serum vitamin D concentrations following exposure to simulated sunlight (the amount required to cause a slight pinkness of the skin) to the whole body was equivalent to ingesting approximately 10,000 to 25,000 IU of vitamin D (6).

People with dark-colored skin synthesize markedly less vitamin D on exposure to sunlight than those with lighter complexion (7).

Additionally, older adults have diminished capacity to synthesize vitamin D from sunlight exposure and frequently use sunscreen or protective clothing in order to prevent skin cancer and sun damage. The application of sunscreen with an SPF factor of 10 reduces production of vitamin D by 90% (8).

In latitudes around 40 degrees north or 40 degrees south (Boston is 42 degrees north), there is insufficient UVB radiation available for vitamin D synthesis from November to early March. Ten degrees farther north or south (Edmonton, Canada), the “vitamin D winter” extends from mid-October to mid-March. It has been estimated that up to 15 minutes of daily sun exposure on the hands, arms, and face around 12 pm throughout the year at 25 degrees latitude (Miami, FL) and during the spring, summer, and fall at 42 degrees (Boston, MA) latitude may provide a light-skinned individual with 1,000 IU of vitamin D (318).

Food Sources

Vitamin D is found naturally in only a few foods, such as some fatty fish (mackerel, salmon, sardines), fish liver oils, eggs from hens that have been fed vitamin D, and mushrooms exposed to sunlight or UV light.


Most vitamin D supplements available without a prescription contain cholecalciferol (vitamin D3).  A meta-analysis of randomized controlled trials suggested that bolus doses of vitamin D2 (ergocalciferol) may not always be as effective as vitamin D3 in raising serum 25-hydroxyvitamin D concentrations, yet no difference in efficacy was found with daily supplementation with vitamin D2 or vitamin D3 (9).

Nonetheless, a 25-week, randomized, double-blind, placebo-controlled trial found daily supplementation with 1,000 IU of vitamin D3 initiated at the end of summer to be more efficacious than vitamin D2 in maintaining summertime concentrations of 25-hydroxyvitamin D during fall and winter months (10).


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Older adults (>50 years)

Daily supplementation with 2,000 IU (50 mg) of vitamin D is especially important for older adults because aging is associated with a reduced capacity to synthesize vitamin D in the skin upon sun exposure.


Ok guys, with the amount of information about D3, it is one of my daily supplements that I take to make sure my body is performing at it’s best. I am takin 4000 – 6000 iu’s daily via supplement form early in the day after my first meal.

Vitamin D is inversely related to melatonin, your sleep hormone. Taking it at night will give you a boost of energy and prevent sleep.


If you take oral vitamin D, you need to also consume in your food or take supplemental vitamin K2. Taking vitamin K2 along with vitamin D slows the progression of arterial calcification, whereas vitamin D alone does not. Vitamin K2 engages in a delicate dance with vitamin D, and you need both in adequate amounts for optimal health. Vitamin D and vitamin K2 work together to produce and activate Matrix GLA Protein (MGP), which congregates around the elastic fibers of your arterial lining, guarding them against calcium crystal formation (15). 

There are several different forms of vitamin K2. MK-8 and MK-9 come primarily from fermented dairy products, like cheese. MK-4 and MK-7 are the two most significant forms of K2 and act very differently in your body.

MK-7, which is the form used in the featured study, is a newer agent with more practical applications because it stays in your body longer; its half-life is three days, meaning you have a much better chance of building up a consistent blood level, compared to MK-4 or vitamin K1.

MK-7 is extracted from the Japanese fermented soy product called natto, and you can obtain all the K2 you’ll need (about 200 micrograms) by eating 15 grams of natto daily, which is half an ounce.

The next best thing to dietary vitamin K2 is a vitamin K2 supplement. MK-7 is the form you’ll want to look for in supplements, because in a supplement form the MK-4 products are actually synthetic.


Have you started taking Vitamin D3? If not then I hope it is something you will consider. But don’t forget to start supplementing with K2 to make sure your body is absorbing the D3 properly.

Are you getting enough Vitamins and Minerals? Did you know that vitamins and minerals have the power to make us super human? Look out for my E-Book coming out in early 2018!


  15. Nephrology Dialysis Transplantation 2013, Volume 28, Issue supple 1, pp 1352-1357 NattoPharma 2013

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