We need vitamin D for strong bones, muscles and overall health. Vitamin D is sometimes called the sunshine vitamin because our bodies produce it in response to sunlight. It can also be found in some foods like fish, eggs and fortified dairy products. If required, it can also be taken in supplement form.
Vitamin D is important for the absorption of calcium from your stomach and for the functioning of calcium in your body. This helps your bones to stay healthy and your muscles to work well.
Low levels of vitamin D are linked to bone conditions such as rickets in children and osteoporosis and osteomalacia in adults.
Low vitamin D levels may also be linked to non-skeletal health conditions, such as colorectal cancer,cardiovascular disease and immune system problems. Researchers are looking into whether increasing vitamin D levels could help prevent any of these conditions, but the evidence is not clear at this stage.
Vitamin D has been shown to help reduce falls and fractures in older people in residential care. More research is needed to see if vitamin D could help reduce falls and fractures in other groups of people.
However, too much vitamin D replacement can lead to high levels, which can actually increase your risk of falls. For this reason, you should only take vitamin D as recommended and prescribed by a doctor.
Where does vitamin D come from?
Vitamin D comes from sunlight, foods containing vitamin D and dietary supplements.
Image credit: Canva
Sensible sun exposure
The body creates vitamin D from direct sunlight on the skin when outdoors. The sun’s ultraviolet B (UVB) rays interact with a protein in the skin, converting it into vitamin D. How much sun you need depends on:
your skin colour
your age, weight and how mobile you are
your risk of skin cancer
how much vitamin D you get from your food
whether you are taking medications – some medications make your skin more sensitive to sunburn
where you are in New Zealand
the season and the time of day
certain medical conditions.
As little as 15 minutes under the sun (without sunscreen), 3 times a week enables your body to make enough vitamin D – but you need to be sensible. Exposing your skin to the sun increases your risks of skin cancer, so don't get sunburnt while you do it. Read more about sensible sun exposure.
Food sources of vitamin D
It's hard to get enough vitamin D through diet alone as what you eat and drink provides only about 5–10% of your vitamin D requirements. It's especially important to think about diet during the winter months when you have less exposure to the sun. Examples of good sources of vitamin D include oily fish (North Sea salmon, tuna, eel and warehou) and milk, yoghurt and margarine that have been fortified with vitamin D.
Vitamin D supplementation is not recommended for most New Zealanders. It is only helpful for people at risk of vitamin D deficiency. See below, who is most at risk of vitamin D deficiency.
How much vitamin D do I need?
Vitamin D is measured in micrograms written as µg, so 5 µg/day means 5 micrograms per day. The amount you need depends on your age and stage of life:
Infants to adults (aged 1–50 years): 5 µg/day.
Adults (aged 51–70 years): 10 µg/day.
Older adults (aged 70+ years): 15 µg/day.
Pregnant and breastfeeding women: 10 µg/day.
What happens if you don't have enough vitamin D?
If you don't have enough vitamin D you may not notice any symptoms at first, but you may get:
pain in your muscles.
An ongoing lack of vitamin D can increase your risk of weak, brittle bones andosteoporosis.
Who is most at risk of vitamin D deficiency?
You are at higher risk of vitamin D deficiency if you:
have dark skin or a condition that prevents you getting sun exposure
wear clothing that covers your skin most of the time for cultural or religious reasons
Your doctor or healthcare provider may recommend a vitamin D test if you are at higher risk of vitamin D deficiency. A test is not always needed before your doctor prescribes a vitamin D supplement. Read more about vitamin D testing.
Can you have too much vitamin D?
It is rare to have toxic levels of vitamin D, but it can happen if you take high levels of vitamin D supplements over a long period of time. If you do this, there is some evidence this will have adverse effects, such as headaches and gastrointestinal disturbance, kidney stones, kidney failure and cardiac arrhythmia. For this reason, you should only take vitamin D supplements as recommended and prescribed by a doctor. Read more about vitamin D supplements for adults.
Dr Helen Kenealy is a geriatrician and general physician working at Counties Manukau DHB. She has a broad range of interests and has worked in a variety of settings including inpatient rehabilitation, orthgeriatrics and community geriatrics.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Helen Kenealy, geriatrician and general physician, CMDHB
Last reviewed: 30 Jun 2020
What is the connection between vitamin D and sensible sun exposure?
Most people get about 80% of their vitamin D from the ultraviolet B (UV-B) rays in sunlight.Most healthy people should be able to get enough vitamin D levels by spending time outdoors during the day.
However, about 5% of adults in New Zealand are lacking in vitamin D. A further 27% are below the recommended blood level of vitamin D.
This means you need to make sure you're getting enough sensible sun exposure. And you can only do this outside, because glass blocks UV-B rays, so sitting by a sunny window doesn't work.
What is sensible sun exposure?
As little as 15 minutes in direct sunlight (without sunscreen) 3 times a week is enough for your body to make the vitamin D you need – but be sensible. Exposing your skin to the sun increases your risk of skin cancer, so make sure you don't get sunburnt.
Image credit: 123rf
If you have a history of skin cancer, or are taking medicines that make your skin more sensitive to sun exposure, you should use sun protection all year: stay in the shade, cover your arms and legs, wear sunglasses and a hat that shades your face and neck, and use sunscreen.
In the warmer months leading up to, during and after summer, exposing yourself to gentle early morning or late afternoon sunlight is recommended.
As little as 6–8 minutes of sun exposure may be enough to produce 1,000 IU of vitamin D.
A daily walk or some other form of outdoor physical activity in the early morning or late afternoon, with your face, arms and hands exposed, could achieve this.
Between 10am and 4pm the sun is too harsh and you should use sun protection: stay in the shade, cover your arms and legs, wear sunglasses and a hat that shades your face and neck and use sunscreen
Between May and August (winter months)
Sun exposure in the cooler months before, during and after winter, is important. Head outside for 30 minutes of sunshine in the middle of the day.
Having dark skin is associated with decreased rates of vitamin D production and people with darker skin may need 3–6 times more sun exposure to get the same level of vitamin D production as people with lighter skin. Talk to your doctor about sensible sun exposure for your skin type.
You can't get vitamin D by sitting inside by a sunny window – UVB waves do not pass through glass. You need to be in direct sunlight.
Using sunbeds to boost vitamin D levels is not recommended. Using sunbeds is associated with an increased risk of melanoma, which rises with greater use and earlier age of first use.
Taking vitamin D supplements is not recommended for most New Zealanders. It is only helpful for people at risk of deficiency, such as if you:
have reduced mobility and are housebound, such as frail older people
have dark-coloured skin
completely cover your skin with clothing or veils
completely avoid the sun for medical reasons, eg, because you have had skin cancer or are using medicines that sensitise you to the sun
live in southern regions of New Zealand, which means you may experience short-lived vitamin D deficiency between the winter months of May and August
are receiving treatment for osteoporosis and need to take calcium supplementation because your dietary calcium intake is inadequate (vitamin D aids the absorption of calcium).
Why should I consult my doctor before starting supplements?
If you think you are at risk, talk to your doctor before taking supplements. Taking supplements under the care and advice of your doctor helps ensure you are getting the full benefit of a supplement. It also minimises the potential for harm that can occur from taking too much of a vitamin or from interactions between supplements and/or medications.
Which supplement should I take and how much do I need?
If your vitamin D levels are low, your doctor may recommend vitamin D supplements such as vitamin D3 (also called colecalciferol) 1.25 mg (50 000 IU) once a month.
If you are at risk of more severe vitamin D deficiency, you will need higher doses of vitamin D supplements (colecalciferol). Examples of such conditions include:
In chronic kidney disease, damage to your kidneys affects the metabolism of vitamin D. People with severe kidney disease may require vitamin D supplements such as alfacalcidol (One alpha®) or calcitriol (Calcitriol-AFT®).
Labtests now performs all funded vitamin D tests in the community. The method used for vitamin D testing is an immunoassay that has excellent precision.
There are several criteria for a vitamin D testing to be approved at Labtests. These include that the:
test be ordered by an endocrinologist, gastroenterologist, bariatric surgeon, rheumatologist, nephrologist, specialist general physician, orthopaedic surgeon, oncologist or a neurologist
test be ordered for specific high risk groups for rickets/osteomalacia (cystic fibrosis, proven malabsorption, bariatric surgery, refugees, deeply pigmented skin, full veil wearers)
test be ordered for the investigation of rickets/osteomalacia, disorders of calcium and phosphate metabolism, osteoporosis or other metabolic bone disease
test be ordered for children less than 16 years
test be ordered for other patients after discussion with, and approval by a Labtests Chemical Pathologist
request form must show the clinical indication for testing.
Various factors can affect plasma vitamin D results, eg, reduced levels of vitamin D binding protein during illness and obesity.
Patients should have a P1NP test first for increased bone turnover if they have isolated ALP elevation. Vitamin D testing is not indicated if P1NP result is normal for age.
For patients with low vitamin D, vitamin D testing may be retested not less than 3 months after starting vitamin D supplementation. No further testing is usually required if an adequate dosage has been established.
Vitamin D and COVID-19
There is some evidence of an association between vitamin D deficiency and increased severity of COVID-19. Ensure going into winter that people who are likely to have low vitamin D levels receive supplementation. This includes older people who are frail, housebound or living in residential care, people with dark skin pigmentation or people with obesity, chronic kidney disease, liver failure or another medical condition that affects vitamin D metabolism. There is no evidence it is effective in treating COVID-19.