Last Updated May 2011
When we discuss diet with our doctor, we are usually told: “For healthy bones, make sure to buy calcium supplements combined with vitamin D or to get some sun exposure every day”. What if I told you this also helps you breathe better?
How Does the Sun Produce Vitamin D? This term represents a group of fat-soluble steroids, and the major forms for bone health are vitamin D2 (VitD2) and vitamin D3 (VitD3). We produce it whenever the 7-dehydrocholesterol in our skin is exposed to ultraviolet light (UVB). Yet, keep in mind that tanning beds only emit 4-10% of the total emissions as UVB, which means that they do not replace natural light. Sufficient intensity occurs all year round in the tropics, but only in the spring and summer in temperate regions. In the absence of sunscreen, 5-15 minute exposure of our face and hands, 2-3 times per week, is sufficient to maintain normal levels.
Did you know that our pets absorb VitD3 by grooming, as the sun transforms the oily secretions accumulating on their fur? So let them groom!
How Much Do We Need? Since we cannot manufacture sufficient VitD3 from the sun during the fall and winter, we rely on diet or supplements. The guidelines published in November 2010 by the Institute of Medicine for Dietary Reference Intakes (DRIs) are:
· Children and adults (0-71 years = 600 IU)
· Adults (> 71 years = 800 IU)
Natural sources of Vitamin D include fish, liver, mushrooms and eggs. Light-exposed mushrooms may provide up to 100% of the recommended daily value as VitD2, which was shown as effective as VitD3 in maintaining normal blood levels of the active form.
Vitamin D3 is a Prohormone. VitD3 reaches the bloodstream, where it is converted into calcidiol during its passage through the liver, then into calcitriol (biologically active form) in the kidneys. As such, patients with liver or kidney disease may have difficulty generating calcitriol, and require higher doses of VitD3 for healthy bones.
How Does Calcitriol Affect our Bones? Calcitriol binds receptors to optimize calcium concentrations in the bloodstream, and to promote healthy bone mineralization, calcium retention and growth. Vitamin D deficiency is diagnosed by low blood levels of precursor calcidiol because of its long half-life (15 days). Subjects with < 15 mg/ml (37.5 nmol/L) calcidiol are at risk of developing bone softening diseases, including rickets in children and osteomalacia in adults, driven by low bone mineral density and osteoporosis.
Monitoring the prohormone calcidiol in the bloodstream may not detect low levels of the active form calcitriol in patients with kidney complications.
Calcidiol Levels Correlate with Lung Function. In April 2010, Dr. Rand Sutherland reported low calcidiol levels in 54 asthmatic patients that were correlated with disease severity in terms of lung function and airway hyperresponsiveness. In December 2010, Dr. Peter Black and Dr. Robert Scragg compared calcidiol levels and lung function in all 14,000 residents enrolled in the National Health and Nutrition Examination Survey, and discovered that subjects with normal calcidiol levels breather better. Among the COPD patients, non-smokers with calcidiol deficiency had 35% worse lung function than ex-smokers with normal levels. In contrast, COPD smokers presented worse lung function than either group regardless of calcidiol levels, suggesting that smoking and vitamin D deficiency affect different aspects of lung physiology.
In February 2011, Dr. Graeme Zosky reported that mice fed on a low VitD3 diet gave birth to offsprings with significantly smaller lungs, resulting in higher airway resistance and lower lung volume, compared to control mice. This is the first hard evidence linking vitamin D deficiency with altered lung structure and deficits in lung function.
“Vitamin D deficiency during pregnancy may impair lung development
in the fetus and predispose to lung complications."
How Does Vitamin D Deficiency Affect Lung Function? The critical role of VitD3 in bone health suggests that low bone density in the thoracic skeleton may provide weak support of respiratory muscle movements during the breathing cycle. Also, curvature of the upper back (kyphosis) caused by osteoporosis has been shown to reduce rib cage mobility and inspiratory muscle function, leading to a reduction in FEV1. In March 2011, Dr. Sundar reported that mice lacking VitD3 receptors develop all symptoms of COPD, including lymphoid aggregates and the excess production of matrix metalloproteinases responsible for tissue damage and the loss of lung function.
These studies suggest that respiratory therapists should test any patient with impaired lung function for circulating levels of calcidiol. Over a dozen clinical trials are underway to test the potential of VitD3 correction therapies for asthma, COPD and cystic fibrosis. This approach may need to be customized for diseases associated with poor intestinal absorption, like cystic fibrosis.
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