It’s winter here in Australia and I see a lot of patients with low Vitamin D levels. Lots of us have been told that we need to stay in the sun for 5-10 minutes and that should be enough but it’s not as simple as that. I have seen a few women that spend their days gardening and get plenty of sunshine yet their levels are still low!
Well, if their liver and/or kidneys are not functioning at optimal level they will not absorb 25OHD, the principal circulating form of Vitamin D. Some signs and symptoms of Vitamin D deficiency are psoriasis, muscle weakness, chronic lower back pain, osteoporosis and increased susceptibility to infections. The chemical cascade of Vitamin D absorption is very long and technical but here are a few points from research article by Daniel Bikle, M.D., PhD. Professor of Medicine, University of California- VA Medical Center, 4150 Clement St. (111N), San Francisco, CA
1. Vitamin D production in the skin under the influence of sunlight (UVB) is maximized at levels of sunlight exposure that do not burn the skin.
2. Further metabolism of vitamin D to its major circulating form (25(OH)D) and hormonal form (1,25(OH)2D) takes place in the liver and kidney, respectively, but also in other tissues where the 1,25(OH)2D produced serves a paracrine/autocrine function: examples include the skin, cells of the immune system, intestinal epithelium, prostate, and breast
3. Parathyroid hormone, FGF23, calcium and phosphate are the major regulators of the renal 1-hydroxylase; regulation of the extra renal 1-hydroxylase differs from that in the kidney and involves cytokines.
4. The major enzyme that catabolizes 25(OH)D and 1,25(OH)2D is the 24-hydroxylase; like the 1-hydroxylase it is tightly controlled in the kidney in a manner opposite to that of the 1-hydroxylase, but like the 1-hydroxylase it is widespread in other tissues where its regulation is different from that of the kidney.
5. Vitamin D and its metabolites are carried in the blood bound to vitamin D binding protein (DBP) and albumin–for most tissues it is the free (ie. unbound) metabolite that enters the cell; however, DBP bound metabolites can enter some cells such as the kidney and parathyroid gland through a megalin/cubilin mechanism.
6. Most but not all actions of 1,25(OH)2D are mediated by the vitamin D receptor (VDR). VDR is a transcription factor that partners with other transcription factors such as retinoid X receptor that when bound to 1,25(OH)2D regulates gene transcription either positively or negatively depending on other cofactors to which it binds.
7. The VDR is found in most cells, not just those involved with bone and mineral homeostasis (ie. bone, gut, kidney) resulting in wide spread actions of 1,25(OH)2D on most physiologic and pathologic processes.
8. Animal studies indicate that vitamin D has beneficial effects on various cancers, blood pressure, heart disease, immunologic disorders, but these non skeletal effects have been difficult to prove in humans.
9.Analogs of 1,25(OH)2D are being developed to achieve specificity for non skeletal
https://www.ncbi.nlm.nih.gov/books/NBK278935/
If this too technical for you here is an easier overview of Vitamin D deficiency from Healthdirect.gov.au
Vitamin D deficiency
What does vitamin D do?
Vitamin D helps your body absorb the calcium it needs to keep your bones and muscles strong and healthy.
Sources of vitamin D
Most Australians get their vitamin D when they expose bare skin to ultraviolet B (UVB) light from the sun.
Food alone cannot provide an adequate amount of vitamin D and most people are reliant on sun exposure to reach recommended levels. Foods that contain small amounts of vitamin D include fatty fish (such as salmon, mackerel and herring), liver, eggs, margarines and some milk products. Infant formula is fortified with vitamin D in Australia.
Sun exposure and vitamin D
The amount of time you need in the sun depends on several things, including where you live, the season, time of day, your skin colour and the amount of skin exposed. However, during summer, most people can get adequate vitamin D from just 5-10 minutes outside. It’s important to avoid the high UV times, so mid-morning or mid afternoon is best. Always follow safe sun guidelines because too much sun can increase your risk of skin cancer and may cause the vitamin D in your skin to break down.
You can find more information about safe sun exposure and vitamin D on our Stay safe in the sun page and from organisations such as the Cancer Council Australia and Osteoporosis Australia.
Never use a solarium to boost vitamin D levels because they emit dangerous levels of ultraviolet (UV) radiation that increase your risk of skin cancer.
What happens if I don’t have enough vitamin D?
Moderate to severe vitamin D deficiency can lead to rickets (soft bones) in infants and children.
Low vitamin D levels can lead to osteoporosis and increase your risk of falls and fractures (broken bones) if you are over 50. Osteoporosis occurs when your bones lose calcium and other minerals, making them fragile and more likely to break. Vitamin D helps your body to absorb calcium, while not having enough can increase your risk of developing osteoporosis.
People with very low levels of vitamin D (moderate to severe deficiency) are the most at risk of developing health problems.
A number of diseases have been linked to low vitamin D levels such as increased risk of death from cardiovascular disease, cognitive impairment in older adults, severe asthma in children and cancer. Research suggests that vitamin D could play a role in the prevention and treatment of a number of different conditions, including type1 and type 2 diabetes, hypertension, glucose intolerance and multiple sclerosis.
Who is at risk of vitamin D deficiency?
You may be at risk of vitamin D deficiency if you:
- stay mostly indoors for health, work or other reasons
- have naturally dark skin
- cover your body for religious or cultural reasons
- avoid the sun for skin protection or due to medical reasons
- are obese
- have a health condition that affects vitamin D absorption from your diet
- take medicines that cause vitamin D to break down
- are a baby of a vitamin D deficient mother.
Do I need a vitamin D test?
You may need a vitamin D test if you are at risk of vitamin D deficiency.
A vitamin D test is a simple blood test that measures a form of vitamin D in your blood called 25-hydroxyvitamin D (25-OHD). This test is usually only done in people at risk of osteoporosis and needs an assessment and referral by a doctor.
Talk to your doctor if you think you need a vitamin D test.
The best time to test for vitamin D is at the end of winter or in early spring when your vitamin D levels are at their lowest.
Choosing Wisely Australia recommends that you do not need routine testing for Vitamin D deficiency unless you are considered specifically at risk.
How is vitamin D deficiency treated?
If you have a mild deficiency then your doctor may recommend a few simple things such as:
- increasing your sun exposure
- increasing dietary calcium
- increasing physical activity
- taking a vitamin D supplement.
If you have a moderate to severe deficiency then you might need to take a high-dose supplement and repeat the blood test in three months’ time. Your doctor will discuss this course of treatment with you.
Some children and teenagers may need to be tested every year if they are identified as having a high risk of deficiency.
Vitamin D supplements
Vitamin D supplements are available over the counter and in different forms, including capsules, tablets, soluble tablets, chewable tablets, powder and liquids. Your doctor or pharmacist can advise you on the best one for you based on the strength of the medicine, the number and type of active ingredients it contains and your reason for taking it.
You can find more information on vitamin D supplements on the NPS MedicineWise website.
Last reviewed: October 2016
https://www.healthdirect.gov.au/vitamin-d-deficiency