It is essential to understand that in order to know how much vitamin D you should be taking, you should get your blood level checked. Unfortunately, very few doctors do the blood test for vitamin D. You can't rely on the media to expose the issue. If and when they do, it will be too late for most of you and you will have suffered decreased bone density and an increased risk of many cancers. But you don't have to wait for the media.

You can read my article on vitamin D testing and get up-to-date on this important topic before it is too late. Unless you are getting significant sun exposure on large amounts of your skin, in fact, I would advise reading the article right now.

Vitamin D is such an important topic that we recently conducted an exclusive interview with one of the top vitamin D researchers in the world, William B. Grant, Ph.D. Here you will get the insights of someone who is on the cutting edge of vitamin D research and knowledgeable about the importance of sun exposure for health. Taking a few minutes to read through the information below will broaden your understanding of this important issue to help you reach higher levels of health.

GRANT: Let me preface this interview by qualifying my background and the information I present. I have a Ph.D. in physics and have worked for 30 years in remote sensing of the atmosphere and studying aerosols and ozone. For the past seven years, I have applied the ecologic approach for the study of dietary and environmental links to chronic diseases and have read the health literature extensively.

Thus, the information presented is based on my best understanding of the situation and may not be fully in accord with views held by others. It appears that the health care community is beginning to awaken to the great importance of vitamin D for optimal health so that better answers to these questions should be available in the next few years.

Also, a few words about "vitamin D." When produced in the skin or ingested, it is a "vitamin" or "prehormone" and essential for life. Just as cholesterol is metabolized into testosterone, precholesterol is turned into cholecalciferol (vitamin D), which is metabolized into what now is looking more and more like a hormone [25(OH)D]. In turn, this is metabolized in the kidneys or other organs into an even more potent hormone [1,25(OH)2D].

Vitamin D is an essential part of the endocrine system [1] as it controls several of the adrenal hormones, growth of cells, production of enzymes and has other direct genomic functions. The key difference in definition is that hormones have DNA receptor sites, and vitamin A is in that family as well as vitamin D, and vitamins are parts of coenzyme systems (not genomic). In a way, vitamins A and D are both vitamins and hormones. Vitamin D is also produced in plants such as algae, as well as mushrooms (which are neither animals nor plants) exposed to ultraviolet-B (UVB) radiation [2, 2a]. Fish obtain their vitamin D from zooplankton and, likely, phytoplankton.

1. In your estimation, how many Americans are likely to be lacking in vitamin D right now?

Based on my study of the Atlas of Cancer Mortality for the United States [3] and the geographic variation of multiple sclerosis among U.S. veterans of WWII, and a reading of the literature, I think that 80 percent to 90 percent of Americans are vitamin D deficient.

Those with the best vitamin D status live in Hawaii and rural regions of the southwest, which have the highest UVB radiation in July [4]. Those with the worst vitamin D status are those with darker skins and those who live in Alaska and urban regions of the northeast. Nearly all Americans are vitamin D deficient in winter/spring when there is not enough UVB reaching the surface.

2. What is the optimal level of vitamin D?

The current understanding is that serum 25(OH)D levels should be in the 30 to 40 ng/ml (75-100 nmol/L) range for cancer prevention and optimal health. The only way to determine one’s 25(OH)D levels is though blood tests, which can be ordered through a physician or nutritionist. However, care should be exercised in choice of a laboratory since the testing methods and quality of the tests may vary. In addition, since 25(OH)D and parathyroid hormone (PTH) are inversely correlated and have opposite effects on calcium in bones, one could also have PTH levels measured.

Dr. Mercola's Comments:

I believe that Dr. Grant is a bit conservative in his recommendation here and I believe that an optimal level of vitamin D is between 45 and 50. I also highly recommend testing though as it is relatively dangerous if one exceeds a vitamin D level of 60. 3. What are some of the diseases that can result if a person’s vitamin D levels are less than optimal? There is a large and growing list of diseases related to vitamin D deficiency. The bone diseases, rickets, osteopenia, osteoporosis and osteomalacia, are well known. The role of vitamin D here is to facilitate the absorption of dietary vitamin D and help with calcium metabolism [5]. Muscle pain and weakness is another [6]. There are about 16 types of internal cancers for which vitamin D is a risk reduction factor [7]. Other diseases include multiple sclerosis [8], type 1 diabetes mellitus [9], rheumatoid arthritis [10] and heart disease [11]. 4. In your article you mention "the time required in the sun [for optimal vitamin D] is probably 15 to 30 minutes per day with at least hands and face exposed in the mid-latitudes during summer." What do you recommend for people who cannot get outside to achieve this exposure, or who live in areas that make it difficult to make vitamin D from the sun? First, note that the 15 to 30 minutes per day generally applies to fair-skinned, thin, younger individuals, with the more of the body exposed, the better. Darker-skinned individuals may require several hours per day. For those unable to derive sufficient vitamin D from solar UVB, artificial UVB lamps are a viable option, as are vitamin D supplements. 5. Do you think that overdosing on vitamin D is a serious concern for people taking vitamin D supplements, or is it relatively difficult to reach dangerous levels? I do--too much can lead to bone loss [12]. In addition, a new study from Finland has shown that those with average values of serum 25(OH)D have lower risks of prostate cancer than those with lower or higher values [13]. My recent ecologic study indicates that high summertime UVB levels are a risk factor for prostate cancer, while low wintertime UVB levels are also a risk factor [14]. 6. Is there an alternative to sun exposure that you feel would give the same benefits in terms of vitamin D? The two viable options are artificial UVB and supplements. If visiting an indoor tanning salon, be sure to ask for the booth with the highest UVB (280-315 nm) to UVA (315-400 nm) ratio since only UVB produces vitamin D. UVA is useful in producing a browner tan. Dietary sources of vitamin D are generally insufficient to produce optimal serum 25-hydroxyvitamin D (25(OH)D) since milk contains only 400 I.U. of vitamin D3 and 800 to 1000 I.U. per day are probably required. Fish oil with vitamin D can be consumed, but one should see whether and how much vitamin A is included. Vitamins A and D interact and one does not want too much vitamin A [15]. Dr. Mercola's Comment: While sun tanning booths can clearly increase one’s UVB exposure it does come with some risks. There are X-rays emitted from the ends of the bulbs so ideally lead tape should be wrapped around the bulb ends. Additionally the magnetic ballast that provides the current to the fluorescent bulbs emits high levels of EMF radiation that is likely linked to certain cancers. Because of these conditions I would strongly advise against nearly all commercial sun tanning booths. However, if the above criteria are met then they should be fine, because the actual light and UV exposure from the bulbs is relatively safe if applied with wisdom and caution. 7. Are there symptoms of inadequate vitamin D levels before a person reaches extreme deficiency or becomes sick with a related illness? In other words, would someone be able to tell if they were lacking vitamin D without receiving a blood test? Not really, although there are several symptoms of disease onset that one can look for. One is muscle pain, especially in winter [16]. Another is easily fractured bones. However, even these symptoms are evidence of serious vitamin D deficiency and illness. 8. What is your opinion of sunscreens and sunblocks? Should they be used or do they block the beneficial effects of the sun? The use of sunscreens is good at the beginning of the sunny season if one spends much time out of doors and also for those with fair skin in very sunny climates. The tan that develops with sun exposure is nature’s way of protecting against too much UV radiation. However, constant application of sunscreens reduces the photoproduction of vitamin D [17]. It should be noted that skin pigmentation adapts over periods of millennia to local solar UV radiation (UVR) [18]. The problem in the United States, Australia and New Zealand is that most of the inhabitants have their ancestry in northern Europe, where pale skin is required for optimal vitamin D production. The optimal skin pigmentation for solar UVR levels typical of the latitudes for the United States would be closer to that of those from Southeast Asia and the Middle East, i.e., more olive in complexion. Dr. Mercola's Comment: I believe Dr. Grant is not aware of some of the other concerns about sunscreens that I presented in an earlier article.I normally advise against them 9. What food sources of vitamin D do you feel are best in terms of the quality and absorption availability of the vitamin D? Fish--but not all types. Best are probably cold-water ocean fish such as salmon, sardines, herring, and mackerel; milk and now orange juice are now being fortified [19]. To get much D from fish requires consumption of the skin and fat under the skin, around the fins and at the tail. But while these are tidbits for grizzlies, Inuit, Eskimo and Northwest Pacific Indians and other traditional peoples they are not for most in the United States. However, one has to consider the environmental and health consequences of drinking milk and orange juice. Fish bioaccumulate mercury and other toxins, and the world’s fish supply is rapidly being depleted. Not all people are lactose tolerant; milk fat is associated with various diseases such as breast cancer [20]. Orange juice has lots of sucrose and can give rise to reactive hypoglycemia when consumed on an empty stomach. See Fuller and Casparian [2000] for a chart showing the vitamin D content of various foods. 10. Is it possible for the body to store enough vitamin D from summer sun exposure to last through several months of winter? Vitamin D is stored in the blood for a few weeks and in the fat for a few months. Serum 25(OH)D levels generally drop by 20 percent to 30 percent during winter in midlatitudes [21] and the prevalence of hypovitaminosis D increases markedly [22]. Low winter/springtime serum 25(OH)D levels are associated with the development of a number of autoimmune diseases (e.g., autism [23] and type 1 diabetes mellitus [24]) and schizophrenia [25]; cancer detection increases in winter/spring as well [26]). Concluding statement Much has been learned about the role of vitamin D in maintaining optimal health and preventing disease. Unfortunately, the health community has not given enough attention to vitamin D because for years the focus has been on its 'nutritional' role in bone, not its other genomic functions, which were basically unknown, and because when adding 'vitamin' D to foods in the early years to prevent bone problems (in the UK and later in the U.S.) there were many problems of excess, so much so that deaths occurred. Another reason seems to be that vitamin D can be produced by solar UVB, and solar UVR is associated with skin cancer, premature skin aging and cataract formation. I plan to devote much of my efforts in the next few years to furthering the understanding of the role of vitamin D in maintaining optimal health and educating the general public and the health community. You are welcome to follow my progress at my Web site, www.sunarc.org. Related Articles: Breakthrough Updates You Need to Know on Vitamin D Vitamin D Is Not A Vitamin But A Steroid Hormone Precursor Vitamin D Lowers Inflammation Why You Need to Have Your Vitamin D Level Tested Now Vitamin D May Prevent Skin Cancer Vitamin D For MS Patients Footnotes: Holick, 1987; Zouboulis, 2000 Bjorn and Wang, 2000 Devesa et al., 1999 Herman et al., 1999 Holick, 2004 Plotnikoff and Quigley, 2003 Grant, 2002b; submitted Embry, 2004 Zella and Deluca, 2002; Holick, 2004 Merlino et al., 2004 Holick, 2004 Chiricone et al., 2003 Tuohimaa et al., 2004 Grant, in press Johansson and Melhus, 2001 Plotnikoff and Quigley, 2003 Matsuoka et al., 1988 Jablonski and Chaplin, 2000 Tangpricha et al., 2003 Grant, 2002a Nesby-O'Dell et al., 2002 Bhattoa et al., 2003 Mouridsen et al., 1994 Hypponen et al., 2001 Eyles et al., 2003 Robsahm et al., 2004 Holick, 1992 References (Note: the abstracts for most of these papers can be found at PubMed.) 2a. Holick MF. Evolutionary biology and pathology of vitamin D. J Nutr Sci Vitaminol (Tokyo). 1992;Spec No:79-83. Bhattoa HP, Bettembuk P, Ganacharya S, Balogh A. Prevalence and seasonal variation of hypovitaminosis D and its relationship to bone metabolism in community dwelling postmenopausal Hungarian women. Osteoporos Int. 2003 Dec 23 Bjorn LO, Wang T. Vitamin D in an ecological context. Int J Circumpolar Health. 2000;59:26-32. Chiricone D, De Santo NG, Cirillo M. Unusual cases of chronic intoxication by vitamin D. J Nephrol. 2003;16:917-21. Devesa SS, Grauman DJ, Blot WJ, Pennello GA, Hoover RN, Fraumeni JF Jr., Atlas of Cancer Mortality in the United States, 1950-1994. NIH Publication No. 99-4564, 1999. http://cancer.gov/atlasplus/new.html (accessed March 3, 2004). Embry AF. Vitamin D supplementation in the fight against multiple sclerosis. J Orthomolec Med. In press. Eyles D, Brown J, Mackay-Sim A, McGrath J, Feron F. Vitamin D3 and brain development. Neuroscience. 2003;118:641-53. Fuller K, Casparian JM. Vitamin D: Balancing cutaneous and systemic considerations. Southern Medical Journal 2001;94:58-66. Grant WB. An ecologic study of dietary and solar UV-B links to breast carcinoma mortality rates. Cancer. 2002a;94:272-81 Grant WB. An estimate of premature cancer mortality in the United States due to inadequate doses of solar ultraviolet-B radiation, Cancer, 2002b;94:1867-75. Grant WB. Geographic variation of prostate cancer mortality rates in the U.S.A.; implications for prostate cancer risk related to vitamin D. Int. J. Cancer. in press. Herman JR, Krotkov N, Celarier E, Larko E, Labow G. Distribution of UV radiation at the Earth's surface from TOMS-measured UV-backscattered radiances. J Geophys Res-Atmos. 1999;104:12,059-12,076. http://toms.gsfc.nasa.gov/ery_uv/dna_exp.gif (accessed February 25, 2004). Holick MF. Photosynthesis of vitamin D in the skin: effect of environmental and life-style variables. Fed Proc. 1987;46:1876-82. Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004;79:362-71. Hypponen E, Laara E, Reunanen A, Jarvelin MR, Virtanen SM. Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet. 2001;358:1500-3. Jablonski NG, Chaplin G. The evolution of human skin coloration. J Hum Evol. 2000;39:57-106. Johansson S, Melhus H. Vitamin A antagonizes calcium response to vitamin D in man. J Bone Miner Res. 2001;16:1899-905. Matsuoka LY, Wortsman J, Hanifan N, Holick MF. Chronic sunscreen use decreases circulating concentrations of 25-hydroxyvitamin D. A preliminary study. Arch Dermatol. 1988;124:1802-4. Merlino LA, Curtis J, Mikuls TR, et al. Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women's Health Study. Arthritis Rheum. 2004;50:72-7. Mouridsen SE, Nielsen S, Rich B, Isager T. Season of birth in infantile autism and other types of childhood psychoses. Child Psychiatry Hum Dev. 1994;25:31-43. Nesby-O'Dell S, Scanlon KS, Cogswell ME, et al. Hypovitaminosis D prevalence and determinants among African American and white women of reproductive age: third National Health and Nutrition Examination Survey, 1988-1994. Am J Clin Nutr. 2002;76:187-92. Plotnikoff GA, Quigley JM. Prevalence of severe hypovitaminosis D in patients with persistent, nonspecific musculoskeletal pain. Mayo Clin Proc. 2003;78:1463-70. Robsahm TE, Tretli S, Dahlback A, Moan J. Vitamin D(3) from sunlight may improve the prognosis of breast-, colon- and prostate cancer (Norway). Cancer Causes Control. 2004;15:149-58 Tangpricha V, Koutkia P, Rieke SM, Chen TC, Perez AA, Holick MF. Fortification of orange juice with vitamin D: a novel approach for enhancing vitamin D nutritional health. Am J Clin Nutr. 2003;77:1478-83. Tuohimaa P, Tenkanen L, Ahonen M, et al. Both high and low levels of blood vitamin D are associated with a higher prostate cancer risk: a longitudinal, nested case-control study in the Nordic countries. Int J Cancer. 2004;108:104-8. Zella JB, DeLuca HF. Vitamin D and autoimmune diabetes. J Cell Biochem. 2003;88:216-22. Zouboulis CC. Human skin: an independent peripheral endocrine organ. Horm Res. 2000;54:230-42.