The Vitamin D Shield

Every summer we hear how people are soaking up free vitamin D from sun exposure. How did we make the sun connection? Vitamin D deficiency is characterized by rickets in children and osteomalacia in adults and was noted more frequently in people who were not regularly exposed to sunlight or living in crowded, polluted urban areas in Europe and North America in the 19th century. Those most at risk were the elderly in nursing homes who were constrained to spending most of their days indoors and similarly young children who were not taken outdoors frequently.

What is vitamin D?
Since vitamin D is produced by the body, as a result of exposure to the sun, it is classified as both a hormone and a vitamin. Hormones are the body’s clinical messengers, which travel in the bloodstream to a target tissue or organ. Vitamins pertain to any group of organic compounds that are essential for normal growth and nutrition, which need to be consumed in the diet as the body cannot normally make it. Vitamin D is found in food in two forms, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) (Murray 1996). Food sources include cod liver oil, cold-water fish (mackerel, salmon, and herring), butter, egg yolks, fortified dairy, and dark green leafy vegetables. It is interesting to note that wild salmon contains 4 times more vitamin D than farmed salmon and that high phytate (from grains) and fiber content of vegetarian diets may decrease vitamin D absorption (Willis 2008). Skin exposure to sunlight involves the liver and kidneys to produce 1.25-dihydroxycholecalciferol, the most potent form of vitamin D3. Thus individuals with either liver or kidney diseases may have sub-optimal levels of vitamin D3 due to impaired conversion, which is needed whether vitamin D is obtained from food or via sun exposure.

Why is vitamin D important?
Vitamin D is essential in the absorption of calcium. Calcium is the mineral that builds strong bone and teeth and conditions associated with low vitamin D status include:
• Fractures
• Multiple sclerosis
• Diabetes
• Cardiovascular health
• Immune related disorders
• Colorectal, pancreatic, gastrointestinal, and breast cancer (LoPiccolo 2010)
• Back pain (Willis 2008)

In vitamin D deficient animals intestinal absorption of calcium is reduced by more than 75% (Fleet 2010). Without adequate vitamin D available only 10-15% of dietary calcium is absorbed (Zhang 2010). Therefore calcium and vitamin D go together like birds and a feather.

Factors that affect vitamin D status via sun exposure (Willis 2008):
• Ageing
• Skin pigmentation
• Regular sunscreen use (SPF≥15)
• Clothing
• Cloud cover and atmospheric pollution
• Time of day
• Wintertime latitude >35° N or S

The recommended time for sun exposure is 15-20 minutes per day. Normally we venture outside for a walk or outdoor activities with only the face and hands exposed and this is postulated to be adequate exposure for some people, in some places, on some days. However it is not sufficient for all people, in all locations, all of the time. When applied correctly a sunscreen cream with a protection factor (SPF) of 15 or 30 ensures that the user can stay exposed to the sun 5 times longer than when no cream is applied. Thus, it would take 30 minutes of sun exposure when applying a cream with SPF of 30 to achieve the same absorption as someone who has ventured outside unprotected for only 6 minutes (Reddy 2010).

The alternative to sun exposure include oral supplementation, fortified foods or those naturally containing vitamin D, and intramuscular injections which are preferable for patients who cannot absorb oral vitamin D supplements due to a positive bowel disease diagnosis. Supplementation may however be a risk factor if high doses are ingested over a prolonged period of time whereas sun exposure does not result in toxic levels of vitamin D due to biological self-regulation.

At risk group:

  • Breastfed infants;
  • Older adults, because skin loses the ability to synthesize vitamin D in ageing;
  • People who are not regularly exposed to sunlight due to the climate, rigorous photoprotection, or those individuals who practice complete skin coverage due to religious or cultural traditions;
  • Dark skinned people;
  • Patients who suffer from fat malabsorption or obesity. Vitamin D is fat-soluble vitamin and is deposited in body fat stores making it less bio-available in people with large stores of body fat (LoPiccolo 2010).
  •  
    Are we creating our own sun shield?
    We know that sun exposure results in the most potent form of vitamin D3 but are we going a step too far in protecting ourselves from potential sun damage? Incidental sun exposure historically included gardening, harvesting, hanging up the washing to dry, chatting over the garden fence, walking to the shops, outdoor sports, children playing in the playground or indeed ambling around on their bicycles unsupervised.

    Now we either leave the garden to overgrow, pave or pebble the outside space, hire a gardening service or simply have no energy to tackle the foliage that surround our humble abodes. Now we have tumbledryers or hang the washing on the radiators dotted around the house because we spend many hours working away from home and do not want to risk the ever so frequent showers setting us back to a basket of soggy clothes, towels or linen. We prefer to use social media to make contact with other people and largely ignore those people who live around us thereby sparing ourselves time away from the garden hedge. It is the norm now to drive or use public transport for all our shopping needs as we buy such large quantities, which are very difficult to carry back home. Or alternatively we choose to shop online and have the supermarket van make it all the way to our front door once a week at no extra cost. We choose indoor sports or move traditional sports indoors such as tennis, athletics, and swimming again because it is largely dependant on the weather. Mark Cavendish spoke about the hours upon hours of training that the British Olympic cycling team spent in the gym preparing for their roaring success at the London 2012 games. Day after day was spent without so much as a glimpse of the big red dot in the sky. Playtime in schools are so short that most children have just about enough time to get a drink, make a hasty trip to the toilet, and ravage a snack as if it is the 100m men’s Olympic final sprint. The days where children got grass stains or muddy prints on their school uniforms are replaced by the odd ketchup stain on their ties.

    What is the solution?
    If you are concerned about your vitamin D status, especially if you fall into the at risk group, then have your levels tested either via your GP or privately with the help of your nutrition consultant who has access to a reputable laboratory. Despite your results it is advisable to ensure that your vitamin D uptake is adequate. Even normal results do not mean that you have an unlimited supply of vitamin D stored in your body. At some point you will need to refuel, so to speak.

    It is imperative that you do not spend hours in the sun without adequate protection. However, if you have 30 minutes or less per day where you are able to venture outside it is worth wearing a comfortable hat but save the sunscreen for those days when you will spend more time outside. This will maximize your absorption of vitamin D3 from the sun, the most potent form, in the limited time that you will be able to spend outdoors.

    If your lifestyle does not allow you to be out of office during daytime then it is imperative that you venture beyond your comfort zone and include vitamin D rich food choices regularly. Wild salmon is an excellent and tasty dietary source.

    These options should be your first port of call before considering supplementation unless your consultant has decided otherwise. Remember that supplementation is in addition to a healthy diet and lifestyle, not in place of.

    References:
    Fleet JS, Schoch RD (2010) Molecular mechanisms for regulation of intestinal calcium absorption by vitamin D and other factors. Critical Reviews in Clinical Laboratory Sciences, 47(4), pp. 181-195

    LoPiccolo MC, Lim HW (2010) Vitamin D in health and disease. Photodermatology, Photoimmunology & Photomedicine, Vol. 26, pp. 224-229

    Murray, MT (1996) Encyclopedia of Nutritional Supplements, California, Prima Publishing

    Reddy KR, Gilchrest BA (2010) Vitamin D Sufficiency vs. Sun Protection: Must We Choose? Dermatology Nursing, pp. 2-10

    Willis KS, Peterson NJ, Larson-Meyer DE (2008) Should We Be Concerned About the Vitamin D Status of Athletes? International Journal of Sport Nutrition and Exercise Metabolism, Vol 18, pp. 204-224

    Zhang R, Naughton DP (2010) Vitamin D in health and disease: Current perspectives. Nutrition Journal, 9:65

    This article was published in issue 201 of Positive Health On-Line Magazine in December 2012

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