Vitamin D sunlight for nutrition

There has been a lot of focus on vitamin D in recent years, and with good reason. It is a vitamin that provides many health benefits to humans, but is a deficiency that has emerged as a significant national public health issue in Australia.  It is estimated that more than 30% of Australian adults have inadequate vitamin D status.

Part of the reason for this is that the number of foods naturally containing significant amounts of vitamin D is very limited.  It is primarily found in animal foods, such as fatty fish (salmon, herring, mackerel, sardines), eggs, butter, cheese, liver, meat and milk.  However, these foods only provide small amounts.  Most adults are likely to obtain only 5-10% of their vitamin D requirements from food, and a vegan diet in particular cannot meet vitamin D needs.

The good news is that humans are not totally reliant on food sources of vitamin D to gain adequate amounts, as we have the capacity to synthesise the nutrient ourselves.   This is very beneficial for ostomates in particular.  Due to a variety of reasons, absorption of adequate amounts of nutrients is an issue for many ostomates, and so a nutrient that is not dependent on foods sources or intestinal absorption to maintain adequate status is good news!

Sunlight and Vitamin D

The other reason for inadequate vitamin D status in Australia is the very successful public health campaigns recommending that Australians avoid too much sun exposure in order to reduce their risk of skin cancer.  The synthesis of vitamin D depends on ultraviolet rays from the sun shining on a cholesterol precursor in the skin.  This creates a pre-vitamin molecule, which works its way slowly into the body.  The pre-vitamin molecule must then become activated, which occurs through the action of the liver and kidneys.

Skin exposure to sunlight accounts for more than 80% of the vitamin D in the body, but the skin exposure must occur when the sun is directly overhead.   Short periods of sun exposure are more effective at raising vitamin D levels than long periods. It should also be noted that a Sun Protection Factor (SPF) of 8 or higher reduces vitamin D synthesis significantly.  Vitamin D stores from summer synthesis alone are not generally sufficient to meet winter needs, and many people become vitamin D deficient during the winter months.  Interestingly, the sun imposes no risk of vitamin D toxicity, as prolonged exposure to sunlight degrades the cholesterol precursor in the skin, preventing its conversion to the active vitamin.

Vitamin D has many valuable functions in the body, and its effects are widespread.  Vitamin D receptors have been found in cardiac tissue, muscle tissue, the pancreas, the brain, the skin and throughout the immune system.  The nervous system and reproductive organs are also target tissues of vitamin D.

The primary function of vitamin D is to raise blood concentrations of important bone minerals such as calcium and phosphorous.  However, vitamin D has also been shown to maintain muscle strength, having a particularly positive effect on skeletal muscle, and to enhance the immune system’s response to both bacterial and viral agents.  Vitamin D also reduces expression of autoimmune conditions such as Multiple Sclerosis, Crohn’s disease, Rheumatoid Arthritis, and Type 1 Diabetes, and demonstrates an inverse relationship with cancers of the breast, prostate, colon and skin. Therefore, a higher vitamin D status is thought to reduce the incidence and severity of these illnesses.

salmon fatty foods Vitamin D

People who are more vulnerable to Vitamin D deficiency

Some people are at greater risk of developing a vitamin D deficiency than others.  The elderly, sick, debilitated and disabled with lack of access to sunshine are especially vulnerable, as well as those who are in good health but spend little time outdoors.  Elderly people in particular do not always habitually consume foods containing vitamin D, such as fatty fish and milk, and also tend to have inadequate exposure to direct sunlight to synthesise the vitamin.  With advancing age they are also less efficient at synthesising vitamin D on the occasions that they are exposed to the sun because their skin, liver and kidneys lose their capacity to make and activate the vitamin.  A Tasmanian study revealed that 85% of people aged 60 years were vitamin D deficient.

People with malabsorption issues are also at risk of deficiency, which is the case for many ileostomates in particular.  Vitamin D is a fat soluble vitamin, and therefore requires a fat-functioning digestive system to be absorbed from food.  This includes adequate production of bile from the liver and digestive enzymes from the pancreas. Any diseases or issues that affect the ability of these organs to perform their functions will affect absorption of vitamin D from food, including those with chronic kidney failure.

Another group of people at risk of vitamin D deficiency is those with dark skin, as the pigments in dark skin reduce vitamin D synthesis.  It can take up to six times longer for a person with dark skin to produce the same amount of vitamin D as a person with lighter skin.  Another factor that can lead to deficiency of the vitamin is obesity, as the vitamin becomes trapped in the fat cells and is therefore not available to the body.  Infants who are breast fed by vitamin D-deficient mothers are also at risk of deficiency themselves.

How do you know if you are deficient?

Deficiency symptoms for vitamin D include muscle aches and weakness, pain in the lower back, pelvis and legs, and disorders of calcium metabolism such as osteoporosis and osteoarthritis.   Observational studies have also indicated a correlation between low vitamin D status and: neurological issues such as schizophrenia; mental health conditions such as depression; respiratory illnesses such as asthma; diseases of the cardiovascular system (for example high blood pressure and stroke); infectious diseases such as urinary tract infections; autoimmune diseases such as Multiple Sclerosis, Crohn’s Disease, Type 1 Diabetes and Rheumatoid Arthritis; as well as cancers of the breast, prostate, colon, and pancreas.  As I stated earlier, the impact of the vitamin in the body is widespread!

It is therefore important for ostomates to ensure that vitamin D status is adequate in order to be supportive of good general health, especially if the reason for becoming an ostomate is cancer or Crohn’s disease, for example.  In the case of urostomates, poor immunity and repeated urinary tract infections can be an issue and this may be reflective of low vitamin D levels.  Many ostomates also experience mental health issues such as depression, which could also correlate to poor vitamin D status.

Adequate sun exposure is a critical step in the synthesis of vitamin D, and The Cancer Council has developed guidelines on how much sun exposure is appropriate in different regions of Australia.  The trick is to get enough sun exposure at the right time of day to synthesise sufficient vitamin D, but not enough to increase the risk of skin cancer.

Generally, in Australia, the recommendation is for moderately fair-skinned people to walk with arms exposed for 6–7 minutes mid-morning or mid-afternoon in summer, and with as much bare skin exposed as feasible for 7–40 minutes (depending on latitude) at noon in winter on most days.  This is considered likely to be helpful in maintaining adequate vitamin D levels in the body.

However, if vitamin D status is compromised by any of the issues discussed above, then supplementation may be required, and during winter it may be essential. Care needs to be taken in choosing a supplement to ensure it is appropriate and able to be fully absorbed by your intestinal tract after stomal surgery.  If you need assistance in this regard please contact me.

So, when the warmer weather approaches, enjoy the summer sun in order to synthesise some valuable vitamin D.  Just do so safely and appropriately.  Moderation is the key!

Wishing you good health and happy days,


Article by Margaret Allan

Margaret Allan is a qualified Nutritionist who advises Ostomates and the general public on diet and health-related matters. Nutrition for Ostomates provides a range of consulting options - find out more on our Services Page.