1. Found in...
1.1. Vitamin D3 is found in oily fish such as salmon, mackerel,sardines,cod liver oil, eggs, liver and milk
1.2. Sunshine - 30 mins of full body sun exposure by fair skinned people will produce 30,00iu of vitamin D
1.3. In the uk Vitamin D can only be made via sunlight for March to October
2. RNI
2.1. A safe intake of 8.5-10mcg per day for all infants from birth to 1 year
2.2. A safe intake of 10mcg per day for children aged 1-4 years
2.3. An RNI of 10mcg of vitamin D per day for pregnant and lactating women and population groups at increased risk of vitamin D deficiency
2.4. A reference nutrient intake (RNI) of 10mcg (400iu) of vitamin D per day, throughout the year, for everyone in the general population aged 4 and over.
3. Metabolism
3.1. 1. Skin - the action of sunlight on the skin changes a cholesterol derivative precursor 7 dehydrocholesterol into vitamin D3
3.2. 2. The liver converts vitamin D3 into 25-hydroxyvitamin D3
3.3. 3. The kidneys convert vitamin D to its active form 1,25-dihydroxyvitamin D3, which is released into the blood for other tissues to use.
3.4. Parathyroid hormone (PTH) increases the conversion of vitamin D to active form.
3.5. The enzyme that converts vitamin D to its active form is present in the kidneys and in many other cells.
3.6. The action of sunlight on the skin changes a cholesterol derivative precursor - 7 dehydrocholesterol into vitamin D3. This then travels to the liver to convert the vitamin D3 into 25-hydroxyvitamin D3. The kidneys then convert the 25-hydroxyvitamin D3 to its active form 1,25-dihydroxyvitamin D3, which is released into the blood for tissues to use.
4. Vitamin D is stored in large amounts in adipose tissues. THis can lead to a mild deficiency in the obese.
5. Deficiencies
5.1. Rickets, osteomalacia (rickets in adults), bone pain, muscle weakness and poor bone density
5.2. The elderly & other people who don't go out in the sun and people who cover up for cultural reasons all have a far higher risk of vitamin D deficiency.
5.3. Those with dark skins synthesise less vit D and need 3-5 times longer in the sun the make the same amount as a european.
5.4. reduced liver and/or kidney function have a higher risk as both organs play a role in conversion to its active form
5.5. Obesity is a risk factor for vitamin D deficiency as vitamin D is stored away in fat tissue rather than being released into circulation for use.
5.6. Sunscreen prevents the synthesis of vitamin D - e.g. a sunscreen with an SPF of 8, reduces vitamin D production by 95%.
6. Interactions
6.1. Ca - vitamin D works with PTH to regulate plasma Ca levels
6.2. Vitamin D controls Ca absorption, excretion and bone mineralization
6.3. Absorption of Ca is greatly increased in the intestines with there too Vitamin D
6.4. Vit D also enhances Ca uptake in the muscle, which is vital to muscle contraction and relaxation.
6.5. Phosphorous absorption in the gut is enhanced by up to 80%
7. Immunity
7.1. All immune cells have significant quantities of vitamin D receptors and deficiency of vitamin D is associated with an increased risk of infection and an increased risk of auto-immune disease
7.2. Vitamin D is considered immunomodulatory as it increases innate immunity and promotes a more tolerant adaptive immunity.
7.3. Vitamin D stimulates the maturation of Natural Killer (NK) cells and a deficiency contributes to a reduction of NK cells activity
7.4. It has been shown that immune cells, such as macrophages and dendritic cells are able to locally convert 25-hydroxyvitamin D into the active form of vitamin D.
7.5. vitamin D receptor are present on leukocytes, T-helper cells and monocytes and vitamin D3 has been shown to inhibit production of inflammatory markers such as IFN-γ, IL-2, and IL-5 by T-helper 1 lymphocytes
7.5.1. Also differentiation of immune stem cells into monocytes and macrophages takes place in the presence of adequate levels of vitamin D
8. Skin Health
8.1. Acne - vitamin D may have a regulatory effect on sebum producing cells & therefore may be helpful in acne.
8.2. Psoriasis - vitamin D is produced by keratinocytes and regulates keratinocyte differentiation.
9. Uterine Fibroids
9.1. It has been observed that oestrogen suppresses the levels of vitamin D receptor (VDR) and therefore induced the proliferation of fibroid tumour cells, while vitamin D3 significantly reduced the oestrogen-induced proliferation of fibroid tumour cells. It has also been demonstrated that fibroid tumours express reduced levels of VDR in comparison to the adjacent myometrium, suggesting that reduced vitamin D signalling may be a contributing factor in the pathogenesis of uterine fibroids.
10. Roles
10.1. Receptors for vitamin D are found throughout the body
10.2. Bones
10.2.1. Vitamin D is essential for skeletal growth and bone health and maintaining bone mass density, calcium metabolism and immune function.
11. Therapeutics
11.1. Bone mineralisation
11.1.1. Adequate levels of the active form of vitamin D is required for intestinal Ca absorption which promotes Ca absorption in bones.
11.1.2. Severe vitamin D deficiency leads to osteomalacia, whereas less severe deficiency increases the risk of osteoporosis and bone fractures.
11.1.3. On the other hand, high vitamin D levels together with low dietary Ca intake will increase bone resorption and decrease bone mineralization in order to maintain normal serum Ca levels.
11.2. Cancer
11.2.1. Vitamin D may prevent malignancy by down-regulating cancer cell growth and inducing apoptosis
11.2.2. Vitamin D typically promotes cell differentiation and inhibits proliferation
11.3. Depression
11.3.1. lower concentrations of circulating vitamin D are associated with increased likelihood of having depressive symptoms.
11.3.2. Vitamin D receptors and vitamin D activating enzyme 1a-hydroxylase are present in the human brain
11.4. Inflammation
11.4.1. Vitamin D has anti-inflammatory properties as it has beneficial effects on Th1 cell mediated inflammatory conditions.
11.4.2. Vitamin D inhibits synthesis of IL-6 by monocytes, which is the primary stimulant of CRP production in the liver
11.4.3. Vitamin D receptor is present on leukocytes, T-helper cells and monocytes and vitamin D3 has been shown to inhibit production of inflammatory markers such as IFN-γ, IL-2 & IL-5 by T-helper 1 lymphocytes
11.5. Asthma
11.5.1. Vitamin D Supplementation has been shown to inhibit the influx of inflammatory cytokines in the lung, while increasing the secretion of anti-inflammatory IL10 by T-reg cells
11.6. Acne
11.6.1. viramin D may have a regulatory effect on sebum producing cells so could help with acne
11.6.2. Vit D is produced by keratinocytes so can regulate differentiation