Vitamin D: the super vitamin

I’m sure many of you have heard of vitamin D but do you fully understand what it does within your body?

Vitamin D plays a number of import roles within your body which enable normal functioning of a range of metabolic and physiological functions. Insufficient levels of this nutrient can result in disruption to these functions, leading to detrimental effects on our health and also giving rise to various disease states, particularly related to our immune system (1). A number of studies have found links between vitamin D deficiency and adverse health outcomes such as cardiovascular disease, autoimmune diseases, diabetes, cancer and an increased risk of mortality (2). Vitamin D has been shown to be particularly beneficial for our immunity, our fertility and during pregnancy and for our musculoskeletal system, as discussed below.



The need to provide your body with nutrients which the immune system loves is particularly important coming into the winter months – and vitamin D is one of these.

Vitamin D is an immune-system regulator in that it enhances the body’s immune response to both bacterial and viral infections. Vitamin D’s immunomodulation effects work through a number of mechanisms that ensure specific immune cells respond appropriately to pathogens (3). A recent randomised, placebo-controlled and double-blinded study on individuals who frequently experienced respiratory tract infections found significant decreases in the prevalence of infections during a twelve-month period in individuals taking vitamin D supplementation when compared with the placebo group (4). This study demonstrates the beneficial effects of an adequate vitamin D status on strengthening the immune system. Vitamin D also contributes to inhibition of adaptive immunity through its role in down regulating the inflammatory response of specific cells. This mechanism has demonstrated particularly beneficial relevance for autoimmune conditions such as type 1 diabetes, rheumatoid arthritis, multiple sclerosis and Crohn’s disease (3, 5).

Fertility and pregnancy

Vitamin D receptors are found within reproductive tissue including ovaries, endometrium, placenta, testes, spermatozoa and pituitary gland. This suggests vitamin D plays an active role within these tissues (6). Two studies have demonstrated promising effects of increased vitamin D status in women undergoing both donor egg and non-donor egg in-vitro fertilisation (IVF) on achieving clinical pregnancy than women with lower levels of the vitamin (7, 8). Evidence is suggesting vitamin D deficiency may also be the cause of insulin resistance and metabolic syndrome in women with polycystic ovarian syndrome (PCOS), one of the leading causes of female infertility (6). (Read more on PCOS here.)

Vitamin D deficiency in men has been associated with a number of implications regarding sperm quality such as a lower proportion of motile, progressive motile and morphologically normal spermatozoa which can have negative influences on male fertility (2). Vitamin D supplementation has been shown to have beneficial influences on some of these parameters such as motility and progressive motility – in other words, how well sperm swim and the direction in which they swim! (2).

Pregnant women are found to have significantly lower levels of vitamin D than non-pregnant women. Maternal vitamin D deficiency has been associated with an elevated risk of gestational diabetes, pre-eclampsia and bacterial vaginosis, as well as small-for-gestational-age babies and babies with disorders such as rickets, reduced bone density, asthma and schizophrenia (2). Studies on supplementation of vitamin D during pregnancy have shown to be both safe and effective in achieving sufficient vitamin D status. Vitamin D supplementation has demonstrated beneficial health outcomes of reducing the risk of preterm delivery, as well as reducing infections, diabetes mellitus, hypertension and pre-eclampsia in mothers (2).

Musculoskeletal health

Vitamin D plays an integral role in the intestinal absorption of calcium, balancing levels of both calcium and phosphorus in the blood, together with the process of formation and demineralisation of the bones.  As a result of these functions, among others, there is a correlation between decreased vitamin D levels and decreased bone mass density, resulting in conditions such as rickets, osteomalacia, osteoporosis and an increased risk of fracture (6). Vitamin D also plays a role in muscular health and strength, demonstrated through vitamin D deficient individuals experiencing muscular weakness and pain, difficulty walking and increased falls (5).

What are optimal vitamin D levels?

Doctors often refer to having ‘optimal’ levels of vitamin D when concentrations within the blood are within the reference range. But studies have indicated that even levels within this range can result in deficiency symptoms and impaired vitamin D functioning within the body. For this reason, it is important to ensure your levels are considered to be within the ideal range of >100nmol/L to optimise body function and prevent associated deficiency conditions. Due to the essential role vitamin D plays in immune health, as previously discussed, it is vital to ensure levels are also optimal for ensuring your immune system is functioning at its best, especially coming into the winter months (1).

Vitamin D concentration in the blood:

Optimal levels should be >100nmol/L

Mild deficiency is considered at levels 25–50nmol/L

Moderate deficiency considered at levels 12.5–25nmol/L

Severe deficiency considered at levels <12.5nmol/L

How do we get vitamin D and why do we need to test for it?

According to a 2012 national population-based study of Australians aged 25–95 years, 73 per cent of the population had vitamin D levels that were below the ideal range, with nearly one-third of the population being deficient and four per cent of the population having a severe vitamin D deficiency (9). Alongside this, the prevalence of deficiency was more common among women than men and vitamin D status also decreased with age (9). This study also found that levels of vitamin D decreased greatly during winter and spring, with 58 per cent of women and 35 per cent of men in southern regions of Australia being deficient during this time (9).

Vitamin D can be found in the diet most substantially in food sources of animal origin, however dietary intake alone is unlikely to meet your body’s requirements. The key source of vitamin D comes from your body’s ability to synthesise this nutrient within your skin through ultraviolet (UV) radiation produced by the sun (5, 1). Deficiency of vitamin D can be a result of insufficient dietary intake, reduced sun exposure and/or metabolic or malabsorption diseases (3). Due to the primary source of vitamin D being through sunlight exposure, reduced sunlight experienced during winter – particularly in Victoria – reduces the levels able to be made and therefore your vitamin D status may be diminished. For this reason, testing of vitamin D levels prior to winter is extremely important to ensure you are aware of, and maintaining, your levels throughout the cooler months as needed.

How much sunlight exposure do we need to receive adequate vitamin D levels?

From October to March, 10–15 minutes of unprotected sunlight exposure to 15 per cent of the body outside of the hours of 10am to 3pm, 2–3 times per week is sufficient for adequate synthesis of vitamin D (3, 1). However, due to lowered levels of sunlight between March and October, up to one hour is required to maintain adequate vitamin D synthesis during the cooler months (3). Short bursts of sunlight exposure are considered more effective for vitamin D synthesis than longer periods, as excessive UV exposure can inactivate the newly formed vitamin D within the skin (3).

Why you should supplement with vitamin D

Groups at higher risk of vitamin D deficiency (1):

  • people who avoid dairy and processed foods (sources of fortified vitamin D)
  • people who are unable to attain sunlight exposure
  • dark-skinned individuals
  • pregnant women
  • elderly people
  • people with malabsorption conditions such as: irritable bowel syndrome, Crohn’s disease and ulcerative colitis


To discuss this topic in more detail, please contact our naturopath, Karly, at or to make an appointment click here. Please note, Karly recommends bringing any recent blood tests with you to your appointment.



(1) Hechtman, L. 2012, Clinical naturopathic medicine, Elsevier Australia, Chatswood


(3) Braun, L. & Cohen, M. 2010, Herbs & natural supplements: An evidence-based guide, Elsevier Australia, Sydney


(5) Gropper, S. & Smith, J.L. 2016, Advanced nutrition and human metabolism, 6th ed Wadsworth, Cengage Learning