Vitamin D plays an important role in one's health.
Kimberly K. Reed, O.D., F.A.A.O.
A total of 31% of non-Hispanic blacks, 11% of Mexican-Americans and 4% of non-Hispanic whites are vitamin D deficient, says the U.S. Center for Disease Control's Second National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population, released in April. Other sources suggest this may be more prevalent, but the exact figures are hard to pin down due to the lack of a universal vitamin D deficiency definition.
Vitamin D's importance
Vitamin D promotes calcium absorption in the stomach and maintains sufficient serum calcium and phosphate concentrations to allow normal bone mineralization and to preclude hypocalcemic tetany (neuromuscular hyperexcitability that results in carpopedal spasms.)1 In addition, it is required for both bone growth and bone remodeling. Therefore, a vitamin D deficiency can result in rickets in children, which is bone softening and weakening, and osteomalacia in adults, which is also bone softening and can cause secondary hyperparathyroidism with resulting bone loss and osteoporosis.2,3 Also, a vitamin D deficiency has been linked with cancer, Crohn's disease, depression, type 1 diabetes, multiple sclerosis, autism and prostate hyperplasia.4-9 Literally hundreds of other conditions are being evaluated for possible links.1 However, not all sources consistently find the same disease links to vitamin D deficiency.
With regard to ocular conditions, diabetic patients, particularly proliferative DR patients, have lower 25-hydroxyvitamin D levels than those who don't have diabetes.10 Also, emerging evidence suggests vitamin D metabolism deficiencies might be contributory in early age-related macular degeneration (AMD) patients, but again, not all studies agree on this point.8,11-13
Vitamin D sources
Vitamin D comes from cereal, cod liver oil, eggs, liver, margarine, milk, vitamin D orange juice, salmon, sardines, swordfish, tuna, yogurt and mushrooms.1,14 Fortified foods provide the most vitamin D in our diet.15
The most readily available vitamin D source is from the sun's UVB band. The UVB band is blocked when the sun's light enters the earth's atmosphere at an oblique angle (e.g. morning and late afternoon). If your shadow is longer than you are tall when outside, you're not making much vitamin D, says the Vitamin D Council (www.vitamindcouncil.org).
The lighter the skin, the less its melanin content, and melanin blocks UV's entry into the skin where vitamin D is produced. So, fair-skinned individuals need less sun exposure to produce vitamin D than dark-skinned people.
Once vitamin D is formed in the skin, it must undergo two more transformations — first in the liver and next in the kidney — to be biologically useful.1
Recommended Dietary Allowances (RDAs) for Vitamin D
|0-12 months*||400 IU (10 mcg)||400 IU (10 mcg)|
|1-13 years||600 IU (15 mcg)||600 IU (15 mcg)|
|14-18 years||600 IU (15 mcg)||600 IU (15 mcg)||600 IU (15 mcg)||600 IU (15 mcg)|
|19-50 years||600 IU (15 mcg)||600 IU (15 mcg)||600 IU (15 mcg)||600 IU (15 mcg)|
|51-70 years||600 IU (15 mcg)||600 IU (15 mcg)|
|>70 years||800 IU (20 mcg)||800 IU (20 mcg)|
|• Adequate Intake (AI)|
Courtesy Institute of Medicine, Food and Nutrition Board.
In addition to dark skin, aging influences the skin's ability to synthesize vitamin D, and older populations are likely to spend time indoors.1 Region plays a role as well. So, a light-skinned, young individual in a southern region might need just a few minutes in the sun at mid-day to make sufficient vitamin D, while a dark-skinned older person in a northern climate may need a half hour or longer, to make the same amount, says the Vitamin D Council.
The UVB amount a person absorbs also depends on season, air pollution, cloud cover and the presence or absence of sunscreen, the Vitamin D Council says. In fact, SPF factor 8 sunscreen can reduce vitamin D production by up to 95%. Sunscreen's prevalent use is very likely a deficiency contributor.
Because patients tend to see us more often than their primary care doctors, we, as O.D.s, are in the perfect position to ask our patients whether they have had their vitamin D level checked within the past year and thus, prevent the aforementioned potential conditions. Inquiring about this level in diabetic patients, AMD patients, elderly individuals, homebound persons, those who consistently wear head coverings and robes, dark-skinned patients, those who have fat malabsorption and those who are obese or who have undergone gastric bypass surgery is especially important, as research reveals these patients are at risk of a vitamin D deficiency.1 If your patients say they haven't undergone a recent level check, refer them to their primary care doctor for a simple blood test.
It is widely believed a serum concentration of less than 30 ng/mL is likely inadequate for most people, while 50 ng/mL is sufficient for the vast majority.15 Many fall within these two levels, making clinical correlations with “deficiency” and “disease” more challenging. The lack of a standard “fall below” level to define deficiency also contributes to discrepancies in prevalence estimates.
If the primary care doctor believes the patient is vitamin D deficient, he/she may prescribe supplements, which are available in D2 and D3. Both forms raise serum vitamin D, 25(OH)D. The specific dosing recommendations for breast-fed infants are 400 IU until they are weaned to consume at least 1,000mL per day of fortified formula or milk. Older children and adolescents should receive at least 400 IU per day when diets are not rich in vitamin D, and some sources suggest 600 IU per day.15 Adults should be supplemented at relatively higher doses than the Recommended Dietary Allowance, for a period of two-to-three months before being rechecked.16 (See “Recommended Dietary Allowances (RDAs) for Vitamin D,” page 66.)
By informing patients of the links of nutrient deficiency and disease, we are meaningfully participating in promoting their wellness, which creates patient loyalty. OM
1. Office of Dietary Supplements: National Institutes of Health. Dietary Supplement Fact Sheet. Vitamin D. http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ (Accessed 8/17'12')
2. PubMed Health. A.D.A.M. Medical Encyclopedia. Rickets: osteomalacia in children; Vitamin D deficiency; Renal rickets; Hepatic rickets. (Accessed 8/17/12')
3. Second National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population. 2012. National Center for Environmental Health. Division of Laboratory Sciences. www.cdc.gov/nutritionreport/pdf/Nutrition_Book_complete508_final.pdf#zoom=100 (Accessed 8/17/12'
4. Psychology Today. The Breakthrough Depression Solution. Psychological Consequences of Vitamin D Deficiency. Vitamin D supplementation may help depression. Greenblatt JM. www.psycho logytoday.com/blog/the-breakthrough-depression-solution/201111/psychological-consequences-vitamin-d-deficiency (Accessed 8/17/12')
5. Suibhne TN, Cox G, Healy M, et al. Vitamin D deficiency in Crohn's disease: prevalence, risk factors and supplement use in an outpatient setting. J Crohns Colitis. 2012 Mar;6(2):182-8 Epub 2011 Sep 25.
6. Zittermann A, Gumert JF. Nonclassical vitamin D action. Nutrients. 2010 Apr;2(4):408-25. Epub 2010 Mar 25.
7. Kapur S. Phosphorus balance and prostate cancer. Indian J Exp Biol. 1999 Jul;37(7):623-6.
8. Morrison MA, Silveira AC, Huynh N, et al. Systems biology-based analysis implicates a novel role for vitamin D metabolism in the pathogenesis of age-related macular degeneration. Hum Genomics. 2011 Oct;5(6):538-68.
9. Payne JF, Ray R, Watson DG, et al. Vitamin D insufficiency in diabetic retinopathy. Endocr Pract. 2012 Mar-Apr;18(2):185-93.
10. U.S. Department of Agriculture, Agricultural Research Service. 2011. USDA National Nutrient Database for Standard Reference, Release 24. Nutrient Data Laboratory Home Page, www.ars.usda.gov/ba/bhnrc/ndl.
11. Institute of Medicine of The National Academies. Dietary Reference Intakes for Calcium and Vitamin D, November 2010; revised March 2011. (Accessed www.iom.edu/vitamind.)
12. Parekh N, Chappell RJ, Millen AE, et al. Association between vitamin D and age-related macular degeneration in the Third National Health and Nutrition Examination Survey, 1988 through 1994. Arch Ophthalmol. 2007 May;125(5): 661-9.
13. Day S, Acquah K, Platt A, et al. Association of vitamin D deficiency and age-related macular degeneration in medicare beneficiaries. Arch Ophthalmol. 2012 Aug 1;130(8):1070-1.
14. U.S. Department of Agriculture, Agricultural Research Service. 2011. USDA National Nutrient Database for Standard Reference, Release 24. Nutrient Data Laboratory Home Page, http://www.ars. usda.gov/ba/bhnrc/ndl.
15. Institute of Medicine of The National Academies. Dietary Reference Intakes for Calcium and V itamin D, November 2010; revised March 2011. (Accessed www.iom.edu/vitamind.)
16. UptoDate. Patient information: Vitamin D deficiency: beyond the basics. Drezmer, MK; www.uptodate.com; (Accessed 8/20/12')
|DR. REED IS AN ASSOCIATE PROFESSOR AT THE NOVA SOUTHEASTERN UNIVERSITY COLLEGE OF OPTOMETRY IN FORT LAUDERDALE, FLA., A MEMBER OF THE OCULAR NUTRITION SOCIETY AND AUTHOR OF NUMEROUS ARTICLES ON OCULAR NUTRITION, DISEASE AND PHARMACOLOGY, SHE IS ALSO A FREQUENT CONTINUING EDUCATION LECTURER. TO COMMENT ON THIS COLUMN, E-MAIL DR. REED AT KIM REED@NOVA.EDU.|