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Vieth R, Fraser D. Vitamin D insufficiency: no recommended dietary allowance exists for this nutrient. CMAJ. 2002 Jun 11;166(12):1541-2. PMID: 12074121 In fact, current recommendations for vitamin D are not designed to ensure anything. They are simply based on the old, default strategy for setting a nutritional guideline, which is to recommend an amount of nutrient similar to what healthy people are eating. This approach underlies the circular logic behind a familiar refrain about nutrition: "If you eat a good diet, you won't need supplements." By this logic, the answer to the question, "How much nutrient do you need?" is, "Whatever healthy people happen to be eating." The essential point, lost in the confusing terminology of modern nutrient recommendations, is that a recommended daily allowance (RDA) does not yet exist for vitamin D. Instead, the recommendations for it are referred to as "adequate intake" (AI).12,13 The AI for young adults (5 µg or 200 IU) was chosen to approximate twice the average vitamin D intake reported by 52 young women in a questionnaire-based study reported from Omaha, Neb., in 1997.13,14 Because the available evidence was acknowledged as weak, the Food and Nutrition Board of the US Institute of Medicine called its recommendation an AI.

Commonly recommended daily intake of vitamin D is not sufficient if sunlight exposure is limited. Glerup H, Mikkelsen K, Poulsen L, Hass E, Overbeck S, Thomsen J, Charles P, Eriksen EF. J Intern Med. 2000 Feb;247(2):260-8. PMID: 10692090 Conclusions. Severe vitamin D deficiency is prevalent amongst sunlight-deprived individuals living in Denmark. In veiled Arab women, vitamin D deficiency is the result of a combination of limitations in sunlight exposure and a low oral intake of vitamin D. The oral intake of vitamin D amongst veiled ethnic Danish Moslems was, however, very high, at 13.53 µg (approximately 600 IU), but they were still vitamin D-deficient. Our results suggest that the daily oral intake of vitamin D in sunlight-deprived individuals should exceed 600 IU; most probably it should be 1000 IU day-1 to secure a normal level of 25-hydroxyvitamin D. This finding is in contrast with the commonly used RDA (recommended daily allowance) for adults in Europe: 200 IU day-1.

High prevalence of vitamin D deficiency despite supplementation in premenopausal women with breast cancer undergoing adjuvant chemotherapy. Crew KD, Shane E, Cremers S, McMahon DJ, Irani D, Hershman DL. J Clin Oncol. 2009 May 1;27(13):2151-6. Epub 2009 Apr 6. PMID: 19349547 DOI: 10.1200/JCO.2008.19.6162 Conclusion Vitamin D deficiency is highly prevalent in women with breast cancer. The current recommended dietary allowance of vitamin D is too low to increase serum 25-OHD greater than 30 ng/mL. Optimal dosing for bone health and, possibly, improved survival has yet to be determined.

Despite inadequacies in information concerning the minimum prophylactic requirement of vitamin D for all age groups beyond infancy, there is no doubt that a total intake of 400 I.U. per day is adequate to prevent vitamin D deficiency in substantially all normal children from birth through adolescence. Evidence derived from the study of idiopathic hypercalcemia suggests that certain infants excessively sensitive to the toxic action of vitamin D may, on rare occasions, be adversely affected by daily intakes of 3,000 to 4,000 I.U. and sometimes considerably less. Because of the prevalent practice of food fortification in the United States and Canada, there is now a definite possibility that the individual, even the young infant, may ingest considerably more than the recommended vitamin D allowance, and intakes of 2,000 to 3,500 I.U. per day are possible, particularly beyond infancy. Although there has been no specific evidence that intakes of this order produce deleterious effects beyond infancy, it is pointed out that the long-term consequences of this new nutritional situation on older children or adults are entirely unknown.

Evidence continues to pile up that the sunshine vitamin protects against much more than bone-softening rickets. Vitamin D, also found in milk and oily fish, is becoming king, from fighting colds to preventing cancer. \n\nInvestigators at the Medical University of South Carolina shut down part of a National Institutes of Health study that left nursing mothers and infants deficient, even though the mothers received the maximum safe amount of vitamin D allowed by the Institute of Medicine.\n\nBut here's the kicker. New research suggests we're not getting nearly enough, and recommended levels may be woefully inadequate.

Daily duration of vitamin D synthesis in human skin with relation to latitude, total ozone, altitude, ground cover, aerosols and cloud thickness. Engelsen O, Brustad M, Aksnes L, Lund E. Photochem Photobiol. 2005 Nov-Dec;81(6):1287-90. PMID: 16354110 Vitamin D production in human skin occurs only when incident UV radiation exceeds a certain threshold. From simulations of UV irradiances worldwide and throughout the year, we have studied the dependency of the extent and duration of cutaneous vitamin D production in terms of latitude, time, total ozone, clouds, aerosols, surface reflectivity and altitude. For clear atmospheric conditions, no cutaneous vitamin D production occurs at 51 degrees latitude and higher during some periods of the year. At 70 degrees latitude, vitamin D synthesis can be absent for 5 months. Clouds, aerosols and thick ozone events reduce the duration of vitamin D synthesis considerably, and can suppress vitamin D synthesis completely even at the equator. A web page allowing the computation of the duration of cutaneous vitamin D production worldwide throughout the year, for various atmospheric and surface conditions, is available on the Internet at http://zardoz.nilu.no/~olaeng/fastrt/VitD.html and http://zardoz.nilu.no/~olaeng/fastrt/VitD-ez.html. The computational methodology is outlined here.

"Defensins are small cysteine-rich cationic proteins found in both vertebrates and invertebrates. They are active against bacteria, fungi and many enveloped and nonenveloped viruses. They consist of 18-45 amino acids including six (in vertebrates) to 8 conserved cysteine residues. Cells of the immune system contain these peptides to assist in killing phagocytized bacteria, for example in neutrophil granulocytes and almost all epithelial cells. Most defensins function by binding to microbial cell membrane, and once embedded, forming pore-like membrane defects that allow efflux of essential ions and nutrients

The vitamin D-antimicrobial peptide pathway and its role in protection against infection. Gombart AF. Future Microbiol. 2009 Nov;4:1151-65. PMID: 19895218 Vitamin D deficiency has been correlated with increased rates of infection. Since the early 19th century, both environmental (i.e., sunlight) and dietary sources (cod liver) of vitamin D have been identified as treatments for TB. The recent discovery that vitamin D induces antimicrobial peptide gene expression explains, in part, the 'antibiotic' effect of vitamin D and has greatly renewed interest in the ability of vitamin D to improve immune function. Subsequent work indicates that this regulation is biologically important for the response of the innate immune system to wounds and infection and that deficiency may lead to suboptimal responses toward bacterial and viral infections. The regulation of the cathelicidin antimicrobial peptide gene is a human/primate-specific adaptation and is not conserved in other mammals. The capacity of the vitamin D receptor to act as a high-affinity receptor for vitamin D and a low-affinity receptor for secondary bile acids and potentially other novel nutritional compounds suggests that the evolutionary selection to place the cathelicidin gene under control of the vitamin D receptor allows for its regulation under both endocrine and xenobiotic response systems. Future studies in both humans and humanized mouse models will elucidate the importance of this regulation and lead to the development of potential therapeutic applications

"Hypervitaminosis D is a state of vitamin D toxicity. The recommended daily allowance is 400 IU per day. Overdose has been observed at 1925 µg/d (77,000 IU per day). Acute overdose requires between 15,000 µg/d (600,000 IU per day) and 42,000 µg/d (1,680,000 IU per day) over a period of several days to months, with a safe intake level being 250 µg/d (10,000 IU per day).[1] Foods contain low levels, and have not been known to cause overdose. Overdose has occurred due to industrial accidents, for example when incorrectly formulated pills were sold or missing industrial concentrate cans misused as cans of milk. Vitamin D toxicity is unlikely except when certain medical conditions are present, such as primary hyperparathyroidism, sarcoidosis, tuberculosis, and lymphoma."

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