Vitamin D, sun exposure and cancer
Sunlight is the most important source of vitamin D. 1 The amount of sun exposure needed to make enough vitamin D changes from person to person and is affected by things like skin type, time of day and time of year.
Most people in the UK only need to spend a short amount of time in the sun to make enough vitamin D. 2, 4 This is typically less than the time taken to lead to sunburn and a higher risk of skin cancer. 5 It's possible to find a balance between enjoying the beneficial effects of the sun while not increasing the risk of skin cancer.
Once a person makes enough vitamin D, any extra is turned into inactive substances. 6 So heavy sun exposure does not improve vitamin D levels beyond a maximum threshold, but it can increase the risk of skin cancer. 7 Even leading vitamin D researchers advise using sun protection, such as SPF 15 sunscreens, during long or heavy exposures 2.
Vitamin D synthesis is much lower in winter months in countries at higher latitudes like the UK. 8 But as long as a normal vitamin D level has been built up in the summer, studies show that this will combine with stored vitamin D in fatty tissue to prevent deficiency in the winter 8, 9.
There is increasing scientific evidence that getting enough vitamin D could reduce the risk of bowel cancer and possibly breast cancer. 10-12 It is still unclear if vitamin D could protect against other types of cancer as the evidence is still inconsistent. 13
But this approach does not account for differences in individual behaviour, such as how much time people spend in the sun or how often they travel on sunny holidays. These have more of an impact on a person’s sun exposure. 14
Some groups have a higher risk of vitamin D deficiency, including:
- people with naturally brown or black skin, who need more UV radiation to increase their vitamin D levels than Caucasians 15-18.
- people who wear clothing that fully conceals them 18, 19.
- older people who don’t go outside much, since they have a reduced ability to make vitamin D through their skin 2, 15
- pregnant women and breast-feeding babies with vitamin D-deficient mothers 20.
These groups can supplement their vitamin D levels by eating foods rich in vitamin D or taking vitamin supplements. These include:
- oily fish and cod liver oil
- foods fortified with vitamin D including some cereals and dairy products, and
- vitamin D supplements 2, 15.
Refer to your doctor for more advice.
- IARC, Sunscreens. IARC Handbooks of Cancer Prevention. Vol. 5. 2001, Lyon: IARCPress. Link
- Holick, M., Sunlight "D"ilemma: risk of skin cancer or bone disease and muscle weakness. Lancet, 2001. 357: p. 4-6. PubMed
- Griffiths, A.P. and A. Fairney, Effect of phototherapy on serum 25-hydroxyvitamin D in the Antarctic. Eur J Appl Physiol Occup Physiol, 1989. 59(1-2): p. 68-72. PubMed
- Pitson, G.A., D.J. Lugg, and C.R. Roy, Effect of seasonal ultraviolet radiation fluctuations on vitamin D homeostasis during an Antarctic expedition. Eur J Appl Physiol Occup Physiol, 1996. 72(3): p. 231-4. PubMed
- Webb, A.R. and O. Engelsen, Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status. Photochem Photobiol, 2006. PubMed
- Webb, A.R., B.R. DeCosta, and M.F. Holick, Sunlight regulates the cutaneous production of vitamin D3 by causing its photodegradation. J Clin Endocrinol Metab, 1989. 68(5): p. 882-7. PubMed
- Holick, M., Vitamin D., in Modern Nutrition in Health and Disease, M.e.a. Shils, Editor. 1999, Lippincott Williams & Wilkins: New York. p. 329-346. Link
- Heaney, R.P., et al., Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr, 2003. 77(1): p. 204-10. PubMed
- Beadle, P., J. Burton, and J. Leach, Correlation of seasonal variation of 25-hydroxycalciferol with UV radiation dose. Br J Dermatol, 1980. 103: p. 289-93. PubMed
- Giovannucci, E., Vitamin D and Cancer Incidence in the Harvard Cohorts. Ann Epidemiol, 2008. PubMed
- Lappe, J.M., et al., Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr, 2007. 85(6): p. 1586-91. PubMed
- Garland, C.F., et al., Vitamin D and prevention of breast cancer: Pooled analysis. J Steroid Biochem Mol Biol, 2007. 103(3-5): p. 708-11. PubMed
- Moan, J., et al., Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure. Proc Natl Acad Sci U S A, 2008. PubMed
- Berwick, M. and D. Kesler, Ultraviolet radiation exposure, vitamin D, and cancer. Photochem Photobiol, 2005. 81(6): p. 1261-6. PubMed
- Dawson-Hughes, B., Racial/ethnic considerations in making recommendations for vitamin D for adult and elderly men and women. Am J Clin Nutr, 2004. 80: p. 1763S-6S. PubMed
- Shaw, N. and B. Pal, Vitamin D deficiency in UK Asian families: activating a new concern. Archives of Disease in Childhood, 2002. 86: p. 147-149. PubMed
- Glerup, H., et al., Commonly recommended daily intake of vitamin D is not sufficient if sunlight exposure is limited. J Intern Med, 2000. 247: p. 260-8. PubMed
- MacLaughlin, J. and M. Holick, Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest, 1985. 76: p. 1536-8. PubMed
- Holick, M., L. Matsuoka, and J. Wortsman, Age, vitamin D, and solar ultraviolet. Lancet, 1989. 2: p. 1104-5. PubMed
- Hatun, S., et al., Vitamin D deficiency in early infancy. J Nutr, 2005. 135: p. 279-82. PubMed