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Vitamin D

What is vitamin D?

Vitamin D is made up of a group of fat-soluble vitamins that exist in various forms.

  • Vitamin D2 (ergocalciferol or calciferol) is made from provitamin ergosterol inactivated in plants by the action of sunlight (UV radiation).
  • Vitamin D3 (cholecalciferol / cholecalciferol) is present in small amounts in some foods such as oily fish (salmon, sardines, and mackerel), eggs, meat (particularly liver), and foods fortified with vitamin D. More importantly, cholecalciferol is produced on the skin by the action of sunlight (mainly UVB) in a cholesterolderivative compound (7-dehydrocholesterol).
  • 1,25-dihydroxycholecalciferol (calcitriol) is the biologically active hormonal form of vitamin D, which the body uses to build and maintain strong, healthy bones. Calcitriol is converted to cholecalciferol (vitamin D3) in the liver and kidneys.

Therefore, the skin is of unique importance in the synthesis, storage and release of vitamin D into circulation.

What is the relationship between vitamin D and sun exposure?

It is well established that sunlight is an important source of vitamin D as UVB rays from sunlight trigger the manufacture of vitamin D3 in the skin. However, little information is available on how much sunlight is needed to produce enough vitamin D3 to maintain adequate serum Calcitriol levels to build and maintain healthy, strong bones. On the other hand, there is a lot of evidence about the dangers of overexposure to sunlight and its role in causing skin Cancer. There has been much discussion about how to strike a balance between getting enough sunlight to maintain adequate vitamin D levels and avoiding an increased risk of skin cancer.


  1. In most situations, sun protection is required to prevent skin cancer during times when the UV index (UVI) is elevated. At those times when the UVI is greater than or equal to 3, sensitive sunscreen behavior is warranted and is unlikely to put people at risk for vitamin D deficiency.
    When the UVI is low (1 or 2) no sun protection is required.
  2. During the summer months, most people should be able to achieve adequate levels of vitamin D (25-hydroxyvitamin D in the blood) through short, incidental UV exposure outdoors, outside of peak times. of ultraviolet radiation.
    As an example, a person who burns easily in the sun (skin type 1 or 2) may only need 5 minutes of sun exposure each day before 11 a.m. and after 4 p.m. (on the face, hands and forearms) to reaching adequate levels of vitamin D, while someone who tans more easily or has darker skin (skin type 5 or 6) will need more time, for example up to 20 minutes.
    Deliberate exposure at peak UV times is not recommended, as this increases the risk of skin cancer, eye damage, and photoaging.
    Vitamin D production is believed to be most effective while exercising.
    There is no advantage to spending more time in the sun, as it does not increase vitamin D production beyond the initial amount.
    During winter, particularly in southern New Zealand (or northern Europe), when UV radiation levels are dramatically lower, vitamin D status can drop below adequate levels. Additional measures may be required to achieve adequate vitamin D status, particularly for those at risk for vitamin D deficiency. Vitamin D levels in summer influence vitamin D levels in winter because body stores decline in winter .
  3. Certain people are at high risk for skin cancer. They include individuals who have had skin cancer, have received an organ. transplant or are highly sensitive to the sun. People at high risk should have more rigorous sun protection practices, and therefore should discuss their vitamin D requirements with their doctor to determine if dietary supplementation is necessary in lieu of sun exposure.
  4. Some groups in the community are at increased risk for vitamin D deficiency. These include the elderly, babies of mothers with vitamin D deficiency, people who are homebound or in institutional care, people with types darker skinned, those that avoid sun exposure due to photosensitivity disorders and those that cover their skin for religious or cultural reasons.
    People at higher risk for vitamin D deficiency should discuss their status with their doctor.
  5. People who have darker skin (skin types 5 and 6) have a higher risk of vitamin D deficiency and a lower risk of skin cancer.
    This may have implications for the health of Maori, Asian and Pacific communities.

During the winter months, the production of vitamin D is reduced. However, the body can rely on vitamin D stores in tissues for 30 to 60 days, assuming levels are adequate before winter. As summer approaches and more hours of sunlight are available, the skin produces vitamin D to rebuild depleted stores.

What Causes Vitamin D Deficiency?

The classic vitamin D deficiency diseases are rickets and osteomalacia.

Rickets occurs in children with vitamin D deficiency and is a bone disease characterized by softening and weakening of the bones. There is a loss of calcium and phosphate from the bones, which eventually causes the destruction of the supporting matrix. Not only is vitamin D deficiency caused by a lack of exposure to sunlight, it can arise from other factors including:

  • Lack of vitamin D in the diet, especially in people with vegetarian diets who do not take dairy products or foods of animal origin. People with milk allergy or lactose intolerance are also at risk.
  • Associated medical conditions that affect the absorption of vitamin D from the digestive tract.
  • Kidney disorders that prevent the conversion of vitamin D3 to its active hormone form.
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In adults, vitamin D deficiency can lead to osteomalacia, which causes muscle weakness, bone pain, and bone fractures. Initially, symptoms of muscle weakness and bone pain can be subtle and go unnoticed. Long-term uncorrected vitamin D deficiency can lead to osteoporosis.

Some studies have recently been published suggesting possible beneficial effects of sun exposure in preventing or improving the outcome of a number of diseases, such as breast, prostate and colorectal cancer, autoimmune diseases like non-Hodgkin lymphoma and multiple sclerosis, cardiovascular disease and diabetes. The mechanisms that mediate the association are still under investigation. There is currently insufficient evidence to make recommendations related to vitamin D and these diseases, however the recommendations should be revised when new evidence becomes available.

Who is at risk for vitamin D deficiency?

For most people, consuming foods that contain vitamin D or foods fortified with vitamin D and adequate exposure to sunlight is sufficient to maintain healthy levels of vitamin D. However, there are several groups of individuals who may require dietary supplements. and / or monitoring vitamin D levels to ensure they do not become deficient. However, blood tests can be misleading, as the normal level can depend on the time of year - a high level is needed in late summer to ensure vitamin stores last through the winter. A low level in late winter could be quite normal. Blood tests are also quite expensive (around $ 50 per test in New Zealand).

  • Older people: As people age (> 50 years) the skin cannot synthesize vitamin D3 as efficiently and the kidney is less able to convert vitamin D3 to its active form. It has been estimated that up to 30-40% of older adults with hip fractures are deficient in vitamin D.
  • People with limited sun exposure: people who wear robes and cover their heads for religious reasons, people confined to their homes or offices, people who live in northern Europe or southern New Zealand.
  • Darker-skinned individuals: These people have melanin pigment content, which actually reduces the skin's ability to produce vitamin D from sunlight.
  • Some people develop skin diseases in places exposed to the sun and therefore should avoid it.
  • Infants exclusively breastfed: Vitamin D requirements are not met by human (breast) milk alone. In the US, after 2 months of age, supplementation is recommended unless the baby is weaned to receive milk fortified with vitamin D. In Australia and New Zealand, very short periods of exposure to UV rays before 10 am and after 4 pm will provide your baby with enough sunlight to maintain healthy vitamin D levels even with the use of sunscreen.
  • Vitamin D levels are lower in the obese and those with metabolism and insulin resistance syndromes.
  • Fat Malabsorption Disorders: Vitamin D is a fat-soluble vitamin, so people who have a reduced ability to absorb fat from the diet are at risk.

The normal use of normal sunscreen has not been associated with vitamin D insufficiency in most studies (Matsouka et al. 1987, Farrerons et al. 2001, Marks et al. 1995, Norval et al. 2009). This may be because insufficient sunscreen is applied and sunscreen users may be exposed to more sun than non-users (Im et al 2010).

What is the dose of supplemental vitamin D?

Supplemental vitamin D can be taken in two forms: vitamin D2 and vitamin D3.

  • Vitamin D2 (ergocalciferol): the dose is 400 to 1000 iu per day.
  • Vitamin D3 (cholecalciferol): the usual dose is 1.25 mg (50,000 iu) once a month.

Can You Get Too Much Vitamin D?

Too much vitamin D can cause toxicity leading to nausea, vomiting, poor appetite, constipation, weakness, and weight loss. It can also raise calcium levels in the blood, causing changes in mental status, such as confusion and heart rhythm abnormalities.

Sun exposure is unlikely to cause vitamin D toxicity. Other compounds produced in the skin protect the body from synthesizing too much vitamin D during periods of prolonged sun exposure. Vitamin D toxicity is likely to occur from overdosing on vitamin D supplements. Individuals taking vitamin D supplements should never exceed the recommended dose and should be aware of the side effects of vitamin D overdose.

Why do dermatologists say that unprotected sun exposure is not safe for increasing vitamin D?

UVB radiation has the dual effect of promoting the synthesis of vitamin D3 in the skin (which can be further converted to 1,25 (OH) 2D3) and increasing DNA damage, leading to skin cancer. So though UVR may be an efficient means of providing the nutritional requirement for vitamin D, the advantage for the skin may be offset by the increased risk of mutations.1


  • Childhood is a critical time to reduce exposure to ultraviolet rays and the risk of skin cancer throughout life.2
  • Responsiveness to UVB radiation varies between people, causing some to be low in vitamin D despite heavy sun exposure.3
  • The high level of vitamin D cannot counteract the risks of high sun exposure that leads to skin cancer.4 4
  • Although sunscreens could almost completely block the production of cutaneous Previtamin D3 for theoretical reasons or if administered under strictly controlled conditions has not been shown to do so in practice.5 5
  • Exposure to a small amount of UV produces vitamin D production without sunburn. Exposure to a higher dose does not produce higher amounts of vitamin D; instead, inactive luminsterol and tachysterol are produced. But exposure to large doses of UV causes blistering and peeling sunburns.6 6