Vitamin D, The Sunshine Superhormone
Dr Peter J Lewis, Australia - Updated 15.04.10
The following is extracted from the PDF at the bottom of this page
Vitamin D is not a true vitamin, as it is not an essential dietary factor - it is actually a hormone precursor that is normally produced in the skin through the action of sunlight (UVB) on 7- dehydrocholesterol.
Vitamin D3, made in the skin, is transported to the liver where it is metabolised to 25-hydroxyvitamin D [25(OH)D; aka calcidiol], the major circulating form. Further metabolism occurs in the kidney (and throughout the body) to form the highly biologically active 1,25-dihydroxyvitamin D [1,25(OH)2D; aka calcitriol].
Vitamin D is stored in fat, and excess oral vitamin D is excreted in the bile.
It is largely through historical accident that vitamin D was classified in the early 1920s as a vitamin rather than a steroid hormone.
The molecular structure of vitamin D is closely related to that of classic steroid hormones (e.g. oestradiol, progesterone, testosterone, DHEA and cortisol). 1,25(OH)2D is the most potent steroid hormone in the human body, active at 1/1,000,000,000,000 of a gram!
Actions
Regulates blood calcium levels
- Stimulates intestinal calcium absorption
- Stimulates bone calcium release
- Stimulates resorption of calcium from the kidneys
Increases magnesium absorption
Regulates osteoblasts (bone-building cells)
- 1,25(OH)2D stimulates differentiation of osteoblasts (but high levels may have inhibitory effect)
Regulates osteoclasts (bone resorbing cells)
- 1,25(OH)2D toxic levels stimulates formation and function of osteoclasts
- 24,24(OH)2D inhibits formation and function of osteoclasts
Stimulates synthesis of osteocalcin (a bone protein)
Maintains healthy cartilage
- Regulates chondrocyte proliferation and proteoglycan synthesis
Helps maintain optimal muscle strength
Antioxidant
Anti-inflammatory
- Inhibits cyclooxygenase-2 (COX-2)
- Lowers CRP and IL-6, two measures of inflammation in the body
Reproduction
- Essential for normal reproductive function in both sexes
- important for spermatogenesis and maturation of spermatozoa
- Important for implantation and successful maintenance of pregnancy
- Crucial for normal foetal growth and optimal development of the foetal brain, lungs, skeleton and immune system
Anti-cancer properties
- Antiproliferative (inhibits cancer cell proliferation)
- Prodifferentiating (induces cancer cell differentiation)
- Proapoptotic (induces apoptosis - programmed cell death)
- Antiangiogenic (inhibits angiogenesis - new blood vessel formation)
- Antimetastatic (inhibits metastasis)
- Immunomodulating
- Inhibits COX-2
- potentiates the anticancer effects of many cytotoxic and antiproliferative anticancer agents
- Down-regulates oestrogen receptor levels and decreases growth- stimulatory effect of oestradiol on breast cancer cells
Blood sugar control
- Improves insulin sensitivity
- Stimulates insulin secretion
Inhibits leptin secretion by adipose tissue
Modulates immune function
- Enhances activity of immune cells that have vitamin D receptors
- Regulates synthesis and action of naturally occurring defense in molecules against bacterial antigens
- Regulates antimicrobial peptides in the skin
- Also dampens immune activity in some circumstances
Cardiovascular
- Regulates blood pressure; inhibits rennin synthesis in the kidney
- Improves endothelial function; modulates vascular tone
- Improves cardiac function
- Antihypertrophic role in the heart
- May suppress cardiovascular risk markers (e.g. CRP)
- Anti-atherosclerotic activity
Thyroid
- Affects thyroid function
Multiple functions in the nervous system
- brain development
- adult brain function
- neuroprotective
- antiepileptic effects
- anticalcification effects,
- neuro-immunomodulation
- interplay with neurotransmitters and hormones
- modulation of behaviors
- brain ageing
Has mood modulating effects
- Helps relieve symptoms of depression
Involved in energy metabolism
Important for normal balance
Promotes production of IGF-1 (insulin- like growth factor)
Regulates proliferation and differentiation of keratinocytes (skin cells)
Important in the maturation of the hair follicle
Anti-thrombotic (reduces blood clots)
Most tissues and cells in the body have receptors for vitamin D (VDRs), including:
Bone (osteoblasts, osteoclasts, bone marrow)
Cartilage (chondrocytes)
Muscle
Kidney
Adrenal
Thyroid
Parathyroid
Skin
Hair follicles
Fat cells (adipocytes)
Immune cells
Thymus
Breast
Ovary, uterus, cervix, fallopian tubes
Placenta
Testes, sperm
Prostate
Stomach, small intestine, colon
Pancreas (beta cell)
Liver
Lung
Heart and blood vessels
Brain, pituitary
Inner ear (semicircular canal)
Cancer cells (many)
Sources
Sunlight:
For people living in Australia, the main source of vitamin D is through exposure to sunlight. Studies have shown that between 90-100% of the daily requirement for vitamin D comes simply from being in the sun for about 15-20 minutes a day.
Dietary sources:
Very few foods naturally contain vitamin D, and it is exceptionally difficult to obtain adequate levels of vitamin D solely from the diet. Oily fish, such as salmon, sardines, mackerel and herring are the best sources. Other food sources include shitake mushrooms, egg yolk and fortified foods.
Vitamin D deficiency
Vitamin D deficiency is a global health problem.
A significant number of Australians are deficient in vitamin D - it is a fallacy that Australians receive adequate vitamin D from casual exposure to sunlight.
Risk factors for vitamin D deficiency
Inadequate sun exposure
- Time spent outdoors
- Excessive ˜Slip, Slop, Slap"-ing (using sunscreen can reduce your body's vitamin D production by almost 100%)
- Infants (especially if solely breast fed)
- Elderly
- Dark skin
- Religious/cultural (covered-up style of dress)
- Latitude
- Seasonal variation
- Global dimming (due to atmospheric pollution)
Washing after sun exposure
Ageing
Obesity
Pregnancy
Smoking
Malabsorption e.g. cystic fibrosis, coeliac disease, Crohn's disease
Liver disease (impaired conversion of vitamin D to 25-hydroxy vitamin D)
Kidney failure (impaired conversion of 25-hydroxy vitamin D to 1,25-dihdroxy vitamin D)
Calcium deficiency - results in increased 25-hydroxy vitamin D inactivation in the liver
Some drugs - statins, anticonvulsants, cholestyramine, colestipol, orlistat, ketoconazole
Vitamin A excess may antagonize the actions of vitamin D
Burn injury
Psychiatric disorders
Genetic variability accounts for 25-50% of the variation of vitamin D levels
What are the consequences of lack of vitamin D?
Vitamin D deficiency (hypovitaminosis D) is associated with numerous health problems, including:
Increased inflammation (elevated CRP)
Muscle weakness and pain - hypovitaminosis D myopathy (HDM)
Rotator cuff muscle degeneration
Poor physical performance
Loss of muscle mass with ageing (sarcopenia)
Falls in the elderly
Aches and pains, non-specific musculoskeletal pain
Fibromyalgia (vitamin D deficiency is often misdiagnosed as fibromyalgia)
Fatigue
Chronic low back pain
Osteomalacia bone pain; tenderness on pressing sternum, shinbone, or forearm bone
Sensitive, aching or throbbing teeth
Rickets
Osteopaenia, osteoporosis
Osteoarthritis
Sweaty head as child
Hurting hair during childhood (pain in the scalp when hair is brushed or combed)
Easily tired legs a child
Growing pains in childhood
Periodontal disease, gingivitis
Dental decay (caries)
Anxiety
Depression
Seasonal affective disorder (SAD)
Bipolar disorder
Schizophrenia
Insulin resistance (syndrome X, metabolic syndrome)
Insulin deficiency
Pre-diabetes (impaired glucose tolerance)
Diabetes type 1 and type 2
Diabetic retinopathy
Obesity
Polycystic ovary syndrome (PCOS)
Premenstrual syndrome
Pelvic floor disorders / urinary incontinence in women
Infertility (in men and women)
Pre-eclampsia
Low-birth weight
Seizures in newborns
Hypocalcaemia (low blood calcium)
Auto-immune diseases, including multiple sclerosis, type 1 diabetes, rheumatoid arthritis, Sjogren's syndrome, lupus, Graves' disease, Hashimoto's disease, Crohn's disease, autoimmune prostatitis
Increased susceptibility to infection
Influenza, swine flu
Methicillin-resistant Staphylococcus aureus (MRSA) nasal carriage
HIV disease progression
Psoriasis
Rosacea
Atopic dermatitis
Hair loss (alopecia)
High blood pressure (hypertension)
Peripheral arterial disease
Heart attack (myocardial infarction)
Left ventricular hypertrophy
Congestive heart failure
Cardiomyopathy
Stroke
Asthma
Chronic obstructive pulmonary disease (COPD)
Cystic fibrosis
Renal disease
Multiple sclerosis
Parkinson's disease
Impaired cognitive function in elderly
Alzheimer's disease
Motor neurone disease
Migraine
Tension headache
Retinitis pigmentosa, cataracts, myopia, keratoconus
Hearing loss, otosclerosis, cochlear deafness
Age-related macular degeneration
Increased risk of 17 types of cancer, including
following image is from Causes and consequences of vitamin D deficiency (from BMJ 2008;336:1318-1319)
What should my vitamin D level be?
A blood level of 25-hydroxyvitamin D (25OHD) is the best indicator of vitamin D status.
25OHD level (nmol/L):
<100 = Deficient
100-200 = Ideal
135-225 = Normal in sunny countries
>250 = Excessive
500+ = Potentially toxic
Treatment of vitamin D deficiency
Adequate sun (UVB) exposure (20 minutes/day, without sunscreen)
Diet: increase consumption of oily fish Vitamin D supplementation: Vitamin D3 (cholecalciferol) is the natural form of vitamin D in humans and animals.
To correct a deficiency, 4,000-15,000 IU of D3 a day for 3 months, may be required; thereafter, 2,000-10,000 IU/day will generally be sufficient as a maintenance dose (depending on sun exposure). Maintenance vitamin D supplementation may be taken as a single weekly dose.
Toxicity
Vitamin D toxicity is also known as hypervitaminosis D. All known poisonings with vitamin D3 reflect misuse on an industrial scale. All reports of iatrogenic (doctor-caused) vitamin D intoxification of adults have involved large doses of vitamin D2 or calcitriol.
Safe level (25OHD) < 250 nmol/L
Potentially toxic level (25OHD) 500+ nmol/L [requires a sustained daily intake >/= 40,000 IU]
Resources / further reading
www.vitamindcouncil.org
www.thevitamindcure.com www.vitamindrevolution.com
The Vitamin D Solution: A 3-Step Strategy to Cure Our Most Common Health Problem. Michael F Holick; Hudson Street Press, 2010