Vitamins: Vitamin D Flashcards
Vitamin D:
Why is is strictly not a vitamin?
What is the main source of Vit D?
When is dietary sources required? What foods?
What is the two sources of Vit D called and their abbreviations?
Vitamin D is not strictly a vitamin since it can be synthesised in the skin in response to sunlight
* Dietary sources are only required in the absence of adequate sunlight (UVB), and include two types of vitamin D:
1. Plant source: vitamin D2 (ergocalciferol D2) – found an mushrooms (fungi), but these require good sun exposure
2. Animal source: vitamin D3 is 7-dehydroxycholesterol (cholecalciferol D3) – found in cod liver oil, oily fish (herring, mackerel, sardines, wild-caught salmon) and organic egg yolk
- Vitamin D2 and D3 do not have any direct functions; they both first need to be converted (hydroxylated)
‘ergo’ = plant source D
‘chole’ = animal source D
Pathway
D2 and D3 have the same activation pathway via the liver and then kidney:
Sunlight - Skin (Pro vitamin D) - cholecalciferol (D3) - Liver - 25 (OH) D (calcidiol) - kidneys - 1,25-Calcitriol (active form of vitamin D)
Cholecalciferol D3 and ergocalciferol D2 - intestines - D3 or D2) - liver - 25 (OH) D (calcidiol) - kidneys - 1,25-Calcitriol (active form of vitamin D)
Levels
- Conventional medicine often considers serum ranges (of calcidiol) over 50 nmol/ L to be sufficient
- Below 25 nmol/ L is almost universally agreed to be deficient
- However, the optimal range is generally considered to be 75-125 nmol/ L (some variance).
- So are your clients ‘levels sufficient’ or ‘optimal’?
Vitamin D synthesis from sunlight:
Shadow
When D is lowest / highest?
What UV can penetrate?
Sun exposure
If outside and your shadow is the same height or shorter than you are, you’re getting enough sunlight to make vitamin D.
* Serum levels are usually highest at the end of the summer and lowest at the end of the winter
* Summer: even on cloudy days, UV light can penetrate the clothes and create vitamin D. Sunscreens and window glass block the conversion to vitamin D by blocking UVB radiation
* Winter: Temperate regions may not have adequate UV for synthesis
* 10 minutes of summer sun exposure results in endogenous production of about 400IU in fairer skin types. In darker skin tones it can take 3 - 6 times longer to produce the same amount D3
Endogenous = from within the body
Vitamin D storage
Vitamins D can be stored in the liver four months
Dosage
Our focus should be on first addressing the cause of the deficiency, to avoid a ‘Symptom-based’ approach
* A supplemental dose of 4000 IU / day has been used without adverse effects.
* 1 ug of cholecalciferol = 40 IU
* It is advisable to test vitamin D levels every four months to adjust dosing where appropriate
* Ergocalciferol is less than one-third as potent as cholecalciferol, so D3 is favoured for supplementation. D3 supplements also stay in circulation longer
* Pronounce deficiency (<10 ng / mL): 50,000 IU of vitamin D3 orally once weekly for 2 - 3 months, or 3 times weekly for 1 month
Ug = microgram
Key function - homeostasis
- A key function of vitamin D is to maintain serum calcium and phosphorus homeostasis. This balance impacts many body processes, including heart and nervous system functioning.
- Vitamin D also performs a variety of other functions in the body
Vitamin D Receptor
- The actions of vitamin D are mediated through a nuclear transcription factor known as the vitamin D Receptor (VDR) within the nucleus of each cell. VDR activation is thought to directly and / or indirectly regulate 100 to 1,250 genes
Nuclear = nucleus
Transcription= copying a segment of DNA (a gene)
Bone Health: Functions and therapeutic uses
- Functions:
o Support bone density (along with vitamin K2), by increasing intestinal calcium absorption - Therapeutic uses:
o Osteoporosis
o Osteomalacia and Ricketts
Immune function and regulation: Function and therapeutic uses
- Functions (Support immune function by):
o Enhancing innate immune system
o Regulation of T-helper cells
o Producing antibacterial peptides
o Inhibiting eosinophils
o Reducing inflammatory cytokines (e.g. IL-6 and TNF-a) and prostaglandin production - Therapeutic uses:
o Allergies
o Autoimmunity, e.g. multiple sclerosis
o Infections e.g. viral and bacterial
o Musculoskeletal pain reduction
Cytokines = immune messenger proteins
GIT Health: Functions and therapeutic uses
- Functions:
o The vitamin D receptor (VDR) helps to regulate mucosal inflammation
o Vitamin D has a role in commensal bacterial colonisation
o Intestinal VDR stabilises tight junctions - Therapeutic uses:
o Intestinal inflammation e.g. inflammatory bowel diseases (as well as intestinal permeability)
Anti-cancer: Functions and Therapeutic uses
- Functions:
o Enhances the anti-tumour activity of innate immune cells
o Regulates multiple genes through the VDR, and inhibits angiogenesis - Therapeutic uses:
o Cancer prevention and support
Angiogenesis = blood vessel formation
Insulin:Functions and Therapeutic uses
- Functions:
o Activates transcription of the insulin gene (Increasing insulin secretion)
o Increases cellular sensitivity to insulin - Therapeutic uses
o Diabetes mellitus (type 2, but also type 1)
Vitamins A and D interaction
The balance of vitamin A and D is essential for proper gene transcription.
* The retinoid X receptor (RXR) is a type of nuclear receptor that is activated by vitamin A
* Together VDR/RXR form a complex with DNA for transcription
* So, from a disease prevention approach, maintaining healthy levels of vitamins A and D is crucial for correct gene expression
Deficiency & Signs
- Ricketts and osteomalacia: Demineralised bones. Ricketts occurs in children, whilst osteomalacia affects adults. Presents with bone pain and bowing of lower limb bones.
- Osteoporosis (brittle bones) – fractures
- Severe asthma in children
- Poor immunity or immune dysfunction (autoimmunity, allergies)
- Insomnia
- Nervousness
- Depression
- Menstrual irregularities (increases FSH/LH production)
- Non-specific musculoskeletal pain and fatigue
Osteo = bone
Malacia = softening (from Greek)
