Vitamin D: The sunshine vitamin

Unlike other vitamins, vitamin D is neither exclusively nor prominently available through the diet. Instead, an estimated 90–95% of vitamin D is provided endogenously through skin synthesis after exposure to ultraviolet B (UVB) light from the sun.

But despite an abundance of sunshine in Australia year-round, as our winter season comes to a close each year, it is estimated that almost a quarter of adults have a mild or moderate vitamin D deficiency, with deficiency levels rising to as high as half the population in south-eastern states.

The role of vitamin D

Vitamin D is available through sunlight, food and supplements and it must undergo two chemical processes in the body before it is considered to be biologically active. The first process occurs in the liver when vitamin D is converted to 25-hydroxyvitamin D [25(OH)D], which is also known as calcidiol. The second process occurs predominantly in the kidneys (but also in other tissues) where it is converted to the active form,25-dihydroxyvitamin D [1,25(OH) 2D], also known as calcitriol.

Vitamin D’s role is well established as being essential for musculoskeletal health It is required for calcium absorption in the gastrointestinal tract and plays an important role regulating and utilising serum calcium and phosphorus. For this reason, severe vitamin D deficiency impairs bone mineralisation, presenting as rickets in children and osteomalacia and osteoporosis in adults.

More recently, achieving adequate vitamin D has been found to support good immune health, possibly playing a role in reducing the severity of the flu and protecting against some autoimmune diseases. There is also growing evidence that it may be beneficial in the prevention and treatment of cardiovascular disease respiratory illness and depression—although further research is needed before firm conclusions can be drawn.

How much sunlight is sufficient?

Sun exposure is not without problems, particularly in ‘sunburnt Australia’ where the sun is harsh and skin cancer rates are amongst the highest in the world. It is therefore paramount to balance the incessant risk of overexposure against the need to be exposed to moderate levels of UVB light to maintain adequate levels of Vitamin D.

Realising the importance of facilitating this vital balance, in 2016 a group of national peak health bodies* came together to provide more specific guidelines based on UV index.

• In summer and spring (or when UV index is above 3): 6–7 minutes of sunlight before 10 am or after 2:00 PM on most days of the week.
  
• In the late autumn and winter (or when some parts of southern Australia experience UV index below 3): 20–40 minutes of sunlight in the middle of the day.

To balance sun safety, the Cancer Council recommends that sun protection be used when the UV Index is 3 or above, which can be year-round in northern areas of Australia. Alternatively, when the UV index is below 3, it is advised that it is safe to go outside for short periods of time without sun protection, with the exception of those at high altitudes or near highly reflective surfaces like snow.

Food sources of vitamin D

While diet can also provide vitamin D, intake through diet alone is considered to be insufficient. But this isn’t to say that food intake should be disregarded, as dietary consumption can play an important role in maintaining adequate vitamin D stores. Food that can provide vitamin D includes: plant sources (vitamin D2) such as mushrooms, in particular mushrooms that have been treated with UV radiation; animal sources (vitamin D3) such as oily fish (e.g. salmon, tuna, mackerel), fish oils, egg yolk and beef liver; and fortified foods, which include milks, cereals, breads and margarines.

Supplementation

Serum concentration of calcidiol is currently the best marker for clinical assessment of vitamin D status. While optimal levels of vitamin D are disputed worldwide, Australian organisations generally define levels <29nmol/L as deficient and >50nmol/L as sufficient, with anything in between considered suboptimal.

For patients who are diagnosed with vitamin D deficiency, pharmacists should be recommending supplementation as a means to achieve adequate levels. Currently, Osteoporosis Australia recommends a dose of 3,000–5,000IU/d for 6–12 weeks. Once patients have reached sufficient levels, if appropriate, they should be encouraged to maintain their status through a combination of moderate and safe sun exposure alongside the consumption of vitamin D-containing foods.

For patients who are not vitamin D deficient, but are at risk of vitamin D deficiency, supplementation should be considered at a lower dose. Osteoporosis Australia recommends 1000–2000IU/d. Individuals who are considered at risk of deficiency include:

• people with naturally darker skin
• people who are elderly, housebound or in a residential care facility
• people who cover up for religious or cultural purposes
• people who deliberately avoid sun exposure for cosmetic or health reasons
• people who spend long hours indoors, including people in occupations where they predominantly work indoors
• babies who are born to vitamin D-deficient mothers
• people who have had gastric bypass surgery
• people with anorexia nervosa

For patients who are not vitamin D deficient and are not at high risk of deficiency, there is insufficient evidence to warrant supplementation for general wellbeing.

COVID-19 considerations

Discussions on the importance of vitamin D come at an appropriate time given the current COVID-19 pandemic. As sun exposure is the major determinant of vitamin D status, experts have questioned the impact home isolation may have had on the population levels of vitamin D. In addition, studies have shown a possible association between low vitamin D serum levels and poor lung function, which has spiked interest in the possibility of vitamin D status impacting COVID-19 mortality. There is thought amongst the scientific community that a deficiency in vitamin D could increase one’s risk of contracting COVID-19 or may lead to a more severe disease course.

While data regarding the prevention and treatment of COVID-19 with vitamin D supplementation is not yet available, vitamin D is an essential nutrient, and healthcare professionals should promote recommended intakes of vitamin D for patients who are concerned.

Through being able to recognise those at risk and being familiar with current avenues and recommendations for attaining adequate vitamin D, pharmacists can play an integral role in preventing and treating vitamin D deficiency. Ultimately, pharmacists should be confident in educating and guiding patients towards appropriate supplementation and lifestyle interventions.

*Cancer Council Australia, the Australasian College of Dermatologists, the Australian and New Zealand Bone and Mineral Society, Osteoporosis Australia and the Endocrine Society of Australia

---

Bridget Scrogings

Accredited Practising Dietitian (APD)
Accredited Sports Dietitian