INTRODUCTION: It is a well-established fact that many vitamins regulate body processes and they are useful to prevent and cure some diseases. For instance Vitamin A is important for normal vision and all of the B vitamins help us to get energy from the foods we eat. Vitamin C, vitamin E, and beta-carotene (a precursor of vitamin A) act as antioxidants, and they prevent cells from being damaged by oxygen. Vitamin D is needed for bone health, and Vitamin K is important for blood clotting. Though the popular belief is that Vitamin C is best for fighting cold and preventing respiratory infection, a new research reveals that not getting enough Vitamin D could increase the risk of coming down with a cold or the flu. In this article the importance of vitamin D in human nutrition, and the latest findings on the beneficial effects of Vitamin D to protect the body against cold would be reviewed and discussed.
VITAMIN D IN HUMAN NUTRITION: Vitamin D is a group of fat-soluble prohormones (the precursors to the hormones). Two major forms of vitamin D are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D is found in food, but also can be made in the body after exposure to ultraviolet rays from the sun (Vitamin D3 is produced in skin exposed to sunlight, specifically ultraviolet B or medium wave radiation). Some forms of Vitamin D are relatively inactive in the body, and have limited ability to function as a vitamin. The liver and kidney help convert vitamin D to its active hormone form. The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D has a role in the absorption of calcium, and it helps to form and maintain strong bones. It promotes bone mineralization in concert with a number of other vitamins, minerals, and hormones. Without vitamin D, bones can become thin, brittle, soft, or misshapen. Vitamin D prevents Rickets (in Persian: Narmi Ostokhan) in children and Osteomalacia (in Persian: Narmi Ostokhan) in adults, which are skeletal diseases that result in defects that weaken bones.
Human body gets vitamin D from three sources, which are sunlight, food and supplements:
1. Sunlight: When exposed to sunlight, the skin makes a compound that is converted to vitamin D in the liver and kidneys. People need 10 to 15 minutes of direct sun on their face and arms, without sunscreen, two to three times a week to make enough vitamin D. Those who live in the northern US and Canada need longer time in the sun than those in the South, especially in the winter when the sun is lower in the sky. Several factors affect how well the body makes vitamin D after the skin is exposed to sunlight. The following people may be at risk for vitamin D deficiency: Older people, Persons with dark skin, People with kidney or liver disease, and People who do not get enough direct sun exposure.
2. Food: Eggs, sardines, and salmon contain vitamin D. Most fluid milk and some brands of yogurt are fortified with vitamin D. Fortified breakfast cereals, breads, and orange juice also may contain this vitamin. It is hard to get enough vitamin D from food.
3. Supplements: If you cannot get enough vitamin D from your diet, and you do not get out in the sun much, a supplement can help. It is recommended that older adults and persons with dark skin get extra vitamin D from fortified foods or supplements.
VITAMIN D AS A POSSIBLE CURE FOR COMMON COLD: An article published in the February 23, 2009 issue of the Archives of Internal Medicine revealed an association between lower levels of serum vitamin D and decreased resistance to upper respiratory tract infection (URTI), otherwise known as the common cold. Researchers at Massachusetts General Hospital, Children’s Hospital, Boston, and the University of Colorado analyzed data from 18,883 participants in the Third National Health and Nutrition Examination Survey (NHANES III) of US participants aged 12 and older. Physical examinations following enrollment obtained blood samples and information including the occurrence of recent upper respiratory tract infections. Stored blood samples were analyzed for serum 25-hydroxyvitamin D levels.
Nineteen percent of the participants reported having a recent cold. For those whose serum vitamin D levels were lower than 10 nanograms per milliliter, the incidence was 24 percent, for subjects whose levels were 10 to less than 30 ng/mL the incidence was 20 percent, and the rate dropped to 17 percent among those with levels of 30 ng/mL or higher. After adjustment for demographic and other characteristics, those whose vitamin D levels were lowest experienced a 36 greater risk of URTI, and those whose levels were 10 to less than 30 ng/mL experienced a 24 percent greater risk compared with participants whose levels were at least 30 ng/mL. The association was significantly stronger for those with asthma.
The study is the largest and most nationally representative of its kind to date. “To our knowledge, this is the first population-based study to evaluate and demonstrate an association between serum 25-hydroxyvitamin D level and URTI,” the authors remarked. “The findings of our study support an important role for vitamin D in prevention of common respiratory infections, such as colds and the flu,” concluded lead author Adit Ginde of the University of Colorado Denver Division of Emergency Medicine. “Individuals with common lung diseases, such as asthma or emphysema, may be particularly susceptible to respiratory infections from vitamin D deficiency”. According to Ginde, future research will push recommended vitamin D levels higher: possibly to 2,000 IU a day.
EPILOGUE: In a separate study reported by Sheldon Cohen and a group of researchers, it has been found that sleep quality is thought to be an important predictor of immunity and, in turn, susceptibility to the common cold. There was a graded association with average sleep duration: participants with less than 7 hours of sleep were 2.94 times more likely to develop a cold than those with 8 hours or more of sleep. Poorer sleep efficiency and shorter sleep duration in the weeks preceding exposure to a rhinovirus were associated with lower resistance to cold.
On the basis of research works carried out by Ginde et al and Cohen et al, it may be concluded that people can protect themselves against cold if they get adequate Vitamin D and sleep well!
Manouchehr Saadat Noury, PhD
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