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.
Why is vitamin D important?
Vitamin D maintains the balance of calcium and phosphate within the body, and optimises bone health and muscle function.
Low levels of vitamin D are linked to bone conditions such as rickets in children and osteoporosis and osteomalacia in adults.
There is also an association between low vitamin D levels and other non-skeletal health conditions such as colorectal cancer, cardiovascular disease and immune system problems. We do not yet know if increasing vitamin D levels could help prevent any of these conditions. More research is needed.
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 population groups.
What happens if you don't have enough vitamin D?
If you do not have enough vitamin D you may get:
pain in your muscles
bones that become soft and break (low vitamin D is a risk factor for rickets and osteoporosis).
Link between vitamin D and winter health
The fact that people’s vitamin D levels tend to decrease in the winter when flu cases tend to increase has led researchers to question whether the two might be related. A number of scientific studies have investigated this link:
One study has shown that people with the low vitamin D levels reported having more recent colds or cases of the flu than those with normal levels (1).
In another, children who took vitamin D supplements during the winter months had a 42% lower risk of getting the flu compared to children that did not receive vitamin D (2).
In a third study, children that received vitamin D reported having 50% less acute respiratory infections during the winter-time compared to children that did not receive vitamin D (3).
To date, there has not been enough research to prove a link between vitamin D deficiency and winter colds and flu. However, it stands to reason that if you have low levels of vitamins D, you may be walking around with a weakened immune system, which can leave you susceptible to viral infections.
Who is most at risk of vitamin D deficiency?
Groups at high risk of deficiency include:
older people in both low- and high-level residential care
older people admitted to hospital
people with hip fractures
people with skin cancers or skin-related conditions, where avoidance of sunlight is required
people who completely avoid the sun (eg, because they are on photosensitising medication)
people with malabsorption syndromes
exclusively breastfed infants of mothers with risk factors for vitamin D deficiency.
How much sun you need depends on:
your skin colour
your age, weight and how mobile you are
risk of skin cancer
how much vitamin D you get from your food
if you are taking medications – some medications make your skin more sensitive to sunburn
where you are in New Zealand, season, and time of day
As little as 15 minutes under the sun (without sunscreen), three times a week enables your body to manufacture enough vitamin D – but you need to be sensible. Exposing your skin to the sun increases your risks of skin cancer and it’s important that you should never get sunburnt.
Credits: Editorial team.
Last reviewed: 22 Mar 2017
Sensible sun exposure
As little as 15 minutes in direct sunlight (without sunscreen), three times a week enables your body to manufacture enough vitamin D – but you need to be sensible. Exposing your skin to the sun increases your risks of skin cancer and it’s important that you should never get sunburnt.
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 (shade, cover your arms and legs, and a sun protective hat, sunscreen, sunglasses) all year round. Your doctor may recommend vitamin D tablets for you.
Between September and April (summer months)
In the warmer months leading up to, during and after summer, exposing yourself to gentle early morning or late afternoon sunlight is recommended.
A daily walk or some other form of outdoor physical activity in the early morning or late afternoon, with face, arms and hands exposed, could achieve this. As little as 6 to 8 minutes of sun exposure may be sufficient to produce 1,000 IU of vitamin D.
Between 10am and 4pm the sun is too harsh and sun protection (shade, clothing coverage and a hat that shades the face and neck, sunscreen, sunglasses) should be used.
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.
Dark skin pigmentation is associated with decreased rates of vitamin D production and people with darker skin may require 3 to 6 times more sun exposure to achieve equivalent levels of vitamin D production. Talk to your doctor about sensible sun exposure for your skin type.
You cannot get vitamin D by sitting inside by a sunny window – UVB waves do not pass through glass. You need to be in direct sunlight.
The use of sun beds to boost vitamin D levels is not recommended, as this practice is associated with an increased risk of melanoma, which rises with greater use, and earlier age of first use.
Vitamin D supplementation is not recommended for most New Zealanders.¹ It is only beneficial for people at risk of deficiency. This includes those:¹
with reduced mobility who are housebound such as frail older people
with dark skin colour
who completely cover their skins with clothing or veils
who completely avoid the sun for medical reasons, such as they have had skin cancer or are using medicines that sensitise them to the sun.
who live in southern regions of New Zealand who may experience short-lived vitamin D deficiency between the winter months of May and August.
who are receiving treatment for osteoporosis and need to take calcium supplementation because their 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 will help ensure you are getting the full benefit of a supplement and minimise the potential for harm which may occur from taking too much of a vitamin or from interactions between supplements and/or medications.
Which supplements 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. People at risk of more severe vitamin D deficiency will require higher doses of vitamin D supplements (colecalciferol). Examples of such conditions include:²
malabsorption from the gut
chronic liver disease
In chronic kidney disease, damage to the 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®).
Information for health professionals
The content on this page will be of most interest to clinicians (doctors, nurses, pharmacists, specialists, etc) or those seeking more detail.
Labtests will be performing all funded vitamin D tests in the community starting from 24 June 2019. 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:
test ordered by an endocrinologist, gastroenterologist, bariatric surgeon, rheumatologist, nephrologist, specialist general physician, orthopaedic surgeon, oncologist or a neurologist
test ordered for specific high risk groups for rickets/osteomalacia (cystic fibrosis, proven malabsorption, bariatric surgery, refugees, deeply pigmented skin, full veil wearers)
test ordered for the investigation of rickets/osteomalacia, disorders of calcium and phosphate metabolism, osteoporosis or other metabolic bone disease
test ordered for children less than 16 years
test 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.