Interview conducted by April Cashin-Garbutt, BA Hons (Cantab)
What role does vitamin D play in the body?
The main and well-established role is to do with bone health. We know that vitamin D is important in keeping bones strong.
In the last 30-40 years it has also been realized that vitamin D has a lot of other roles in the body. Vitamin D essentially has a role in any cell in the body that has a vitamin D receptor. Almost all the tissues and organs in the body have been shown to have vitamin D receptors.
What is the body’s main source of vitamin D?
For most people, the body’s main source of vitamin D is sunlight. In Australia, however, people are avoiding the sun; in this case supplements may become their major source of vitamin D.
What levels of vitamin D are normal?
Vitamin D deficiency is considered to be less than 50nmol/L; vitamin D insufficiency is considered to be less than 75nmol/L.
How low do vitamin D levels need to be before a person is considered vitamin D deficient?
Traditionally, vitamin D levels of less than 50nmol/L have been considered as deficient. But many experts advocate sufficient levels as 75mol or above.
What problems can vitamin D deficiency cause?
Bone disease such as osteoporosis and osteomalacia are well known. More recently vitamin D is believed to have a role in many diseases such as cancer, diabetes, MS, depression.
What types of cancer has vitamin D deficiency been associated with?
The strongest evidence is in colorectal cancer. There is also growing evidence in breast cancer. We are not saying that low vitamin D levels cause cancer, but there is an association there.
What we are looking at is whether low vitamin D levels affect prognosis.
What mechanism do you think could explain these associations?
In cancer, they have done cellular studies that have shown that vitamin D stops the way tumors grow or slows down their growth. It is therefore considered an anti-proliferative.
Also, vitamin D helps cells die normally. Cell death can be a problem in some forms of cancer.
How many people were previously thought to be vitamin D deficient?
It was previously assumed most people would maintain adequate vitamin D by casual sun exposure. There were no specific estimates, but the recent research has shown a surprisingly high prevalence of deficiency.
What did your recent research reveal?
Close to 70% of individuals are vitamin D deficient in spring. Women 20-39 years had the highest prevalence of deficiency. Other risk factors were being from a lower socioeconomic background and living in a major city.
Why do you think these people were affected the most?
We can only speculate because we didn’t get the information directly from people. We assume that women of that age group are more likely to use sun screens and stay out of the sun in line with Australia’s Slip-Slop-Slap campaign.
Another explanation is that they are likely to be young mothers who spend lots of time indoors as well.
Why do you think there was a difference between your results and the amount of people previously thought to be vitamin D deficient?
We’re not the only ones to show a high prevalence of deficiency but there are no other large Australian studies looking at vitamin D status – was just based on an assumption that people got enough sunlight in Australia.
What season was vitamin D deficiency most prominent and why do you think this was the case?
Spring. This is because UV levels are at their lowest (maybe because it’s cold and people are not outdoors as much also).
Why do you think vitamin D levels were lower in spring than in winter?
I think this is because we do have some vitamin D stores. These stores are probably continually depleted during the winter months, meaning that vitamin D deficiency is most prominent in spring.
What impact do you think your work will have?
We hope that this will add to evidence to establish guidelines for vitamin D testing and supplementation.
Do you have any plans for further research into this area?
At Westmead Breast Cancer Institute we have established a vitamin D research program. We are currently recruiting for the VIOLET study to determine the effect of vitamin D status at diagnosis on prognostic markers for breast cancer. And we are planning a randomized controlled trial looking at the effect of vitamin D supplementation on chemotherapy related side effects.
How do you think the future of vitamin D deficiency will develop?
We’re working on an online calculator to estimate the risk of deficiency. Hopefully these sorts of tools will allow people to ascertain whether they are likely to have vitamin D deficiency and take appropriate measures to replete their vitamin D levels if appropriate.
Would you like to make any further comments?
We think there need to be guidelines on sensible sun exposure. In Australia we are just told to stay out of the sun in effort to prevent skin cancer, but this has probably led to vitamin D deficiency.
Where can readers find more information?
They can find our paper here: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2265.2012.04398.x/abstract
About Kellie Bilinski
BSc, M Nutr & Diet, APD AN (PhD Candidate)
Kellie is an Accredited Practising Dietitian and Nutritionist with diverse experience in clinical dietetics, private practice, the nutrition industry and research. Kellie currently works as a senior clinical dietitian and research program coordinator at Westmead Breast Cancer Institute, Westmead Hospital in Sydney. She is in the final stages of completing her PhD in The University of Sydney’s Medical School on the effect of vitamin D and metabolic factors such as insulin on cancer growth.
Kellie is regularly speaks at patient forums about the role of diet and nutrition in cancer prevention and during treatment, the health benefits of vitamin D, vitamin supplementation, diabetes, and weight management and about her research at international and national conferences.
Kellie is a dietitian passionate about research into disease prevention through optimal nutrition and translating this into messages for the public and health professionals. She has written several papers that have been published in peer-reviewed journals and regularly writes factsheets and patient information about healthy eating, weight management, and diet and cancer.