http://www.uspharmacist.com/index.a...page=8_1396.htm
Vitamin D
Part II: Low Status and Chronic Diseases
Yadhu N. Singh, PhD
Professor of Pharmacology
College of Pharmacy
South Dakota State University, Brookings, SD
US Pharm. 2004;12:39-49.
The influence of vitamin D on numerous physiological processes is best illustrated by the intimate association between low vitamin D status and various chronic diseases. (The first part of this article, on the need for vitamin D, appeared in the October issue of U.S. Pharmacist.) Selected pathophysiological disorders which are claimed in various publications, many of which are referenced in this article, to be linked to vitamin D deficiency or insufficiency, are listed in TABLE 1. The evidence for some of these claims, derived from representative studies, is discussed below in some detail.
Rheumatoid arthritis: In a recent publication, the Iowa Women's Health Study followed almost 30,000 women over 11 years, during which time 152 of the women developed rheumatoid arthritis (RA). The researchers found that women whose diets were highest in vitamin D had the lowest incidence of RA. In particular, women whose intake of the vitamin was less than 200 IU each day were 33% more likely to develop RA than those who got more.21
Multiple sclerosis: The incidence of multiple sclerosis (MS) is low in the tropics and increases with distance from the equator. It has been suggested that reduced amount of sunlight at higher latitudes, especially during the winter months, is too low to produce adequate amounts of vitamin D. The possible protective effect of dietary vitamin D on the risk of MS was tested in two separate Nurses' Health studies (NHS I: 92,253 subjects followed from 1980 to 2000, and NHS II: 95,310 subjects from 1991 to 2001).22 The data showed a 40% reduction in risk of MS among women who used supplemental vitamin D, compared to women who did not use the supplement. Limitations of the study include the fact that the effect of different amounts of exposure to sunlight was not assessed nor was the blood level of the vitamin measured. However, a study among U.S. veterans found that the average annual hours of sunshine and the average December daily solar radiation at place of birth were strongly and inversely correlated with MS incidence.13 Similar results were obtained in Australia23 and among immigrants to Israel.24
Musculoskeletal disorders: Vitamin D deficiency causes mineralization defects in the growing and adult skeletons, resulting in rickets and osteomalacia, respectively, due to the marked suppression in intestinal Ca absorption and impairment of Ca balance. Osteomalacia is associated not only with mineralization defect of the skeleton but also with isolated or global bone pain, muscle weakness, and muscle pain, which are symptoms that often go undiagnosed or misdiagnosed as some type of collagen vascular disease, such as fibromyalgia. It is now generally agreed that an insufficient vitamin D status also contributes significantly to osteoporosis in the elderly.25 Low calcidiol levels are associated with low Ca absorption rates, hyperparathyroidism, and increased bone turnover leading to bone loss.26,27 In elderly subjects, low circulating calcidiol levels are accompanied by a reduced bone mineral density in the proximal femur.26 Recent studies have also demonstrated that even in female adolescents, insufficient calcidiol levels are associated with low forearm bone mineral density.28
In clinical trials, increase in bone mineral density with vitamin D supplementation was inconclusive, although higher amounts consistently gave a positive effect.15 A large, long-term, randomized controlled trial showed that combined supplements of vitamin D (20 mcg/day) and Ca (1,200 mg/day) were capable of preventing nonvertebral fractures in healthy ambulatory subjects.29 In addition, the bone density of the proximal femur increased 2.7% in the treatment group but decreased 4.6% in the placebo group. However, it is conceivable that the antifracture effect of Ca and vitamin D is not due to their effect on bone mineral density alone. An increase in calcidiol levels may very well improve neuromuscular coordination, as measured by body sway, and may thus decrease the risk of falling and falling-related fractures.15 In a recent study in a residential care facility in Australia, it was found that calcidiol remained independently associated with time to first fall and was reduced by 20% on doubling of the serum calcidiol level.30
Recent evidence indicates that age-related changes in vitamin D concentrations may play a role not only in bone health but also in the loss of muscle mass and muscle strength, also called sarcopenia.31,32 A study just published shows that in both active and inactive ambulatory U.S. men and women over the age of 60, higher concentrations of calcidiol were associated with better musculoskeletal function in the lower extremities. It was found that, for optimal lower extremity function, much improvement occurred at calcidiol concentrations >= 40 nmol/L, with maximum improvement being evident at about 125 nmol/L.33 As almost 80% of the total U.S. population has vitamin D blood levels lower than 50 nmol/L (
www.cholecaciferol-council.com), the findings raise the possibility that muscles of most Americans may benefit from increased levels of vitamin D.
Cardiovascular diseases: Essential hypertension is associated with disturbances in systemic and cellular Ca metabolism and low calcidiol levels. African-Americans, in particular, have a significantly higher prevalence of diastolic hypertension and lower calcidiol serum levels compared with white Americans.34 Short-term daily supplementation with vitamin D significantly reduced diastolic blood pressure, while both systolic and diastolic blood pressure were reduced in mildly hypertensive subjects after six weeks of UV-B exposure.14
Physical activity and an increased intake of unsaturated fatty acids are frequently recommended in the prevention and treatment of cardiovascular diseases. Physical activity is associated with higher circulating levels of calcidiol and calcitriol compared with a sedentary lifestyle.35 Thus the beneficial effect of physical activity may at least in part be due to improved vitamin D status.
Among the many important risk factors for atherosclerosis development, such as hyperlipoproteinemia, altered glucose tolerance, increase in blood coagulation factors, blood viscosity, and leukocyte counts,36 is recently identified C-reactive protein (CRP), which is an important indicator of inflammatory reactions. There is strong evidence that atherosclerosis is a low-grade systemic inflammatory disease.37 Low vitamin D status and elevated CRP levels have been linked to increased cardiovascular morbidity, which could be alleviated by vitamin D supplementation or UV exposure, even in critically ill patients. Even a low dose (500 IU/d) lowered CRP by more than 25% in one small group of such patients.38
Diabetes mellitus: The dependence of normal insulin secretion in pancreatic ß-cells on vitamin D has been known for many decades. Studies show that low vitamin D activity can result in both increased insulin resistance and reduced insulin secretion. In addition, there was a fourfold to fivefold higher prevalence of type 2 diabetes in dark-skinned Asian immigrants in comparison to British Caucasians in London, indicating that low vitamin status may contribute to diabetes pathogenesis.39 In a Norwegian study, it was found that daily intake of cod liver oil, which is extremely high in vitamin D content, during pregnancy can reduce the risk of diabetes in the offspring,40 while in Finland regular vitamin D supplementation of 50 mcg/d during infancy in the 1960s was associated with a marked reduction in the risk of type 1 diabetes 30 years later in comparison with unsupplemented infants.41
It should be mentioned that diabetes mellitus, hypertension, and cardiovascular diseases are associated with obesity. Obese individuals, as a group, have low plasma concentrations of calcidiol.42,43 While the reason for this is unknown, a number of possible causes have been mentioned, including lifestyle-dependent reduced exposure to UV light, reduced vitamin D ingestion, and negative feedback control by calcitriol on hepatic formation of calcidiol. Researchers recently evaluated the possibility that the deficiency may be due to vitamin D uptake and storage in adipose tissue.44 In agreement with previous studies, they found that, on UV-B irradiation or an oral challenge with vitamin D, the blood level of vitamin D in obese patients was more than 50% lower than in nonobese counterparts. They concluded that obesity-associated vitamin D insufficiency is likely due to the decreased bioavailability of vitamin D and metabolites from cutaneous and dietary sources because of their deposition in body fat compartments.
Cancer: Since most human cancers develop over long periods of time, it becomes difficult to perform reliable intervention studies on the association between vitamin D and cancer risks. However, there is sufficient evidence to conclude that enhanced sunlight exposure is associated with lower incidence of at least a dozen different cancers, in particular, colon, breast, prostate, ovary, uterus, bladder, esophagus, stomach, and rectal cancer.45 The strongest evidence for a protective role for vitamin D in colon or colorectal cancer rests on inverse associations between vitamin D intake and incidence of these cancers. A nested case-control study based on serum drawn from a cohort of 26,620 individuals reported that serum concentrations of calcidiol in the range of 65 to 100 nmol/L were associated with large reductions in the incidence of colo-rectal cancer compared with lower calcidiol levels.46
The NHANES I epidemiological study using several measures of sunlight exposure and dietary vitamin D intake indicates substantially reduced risk of breast cancer. The risk reduction was highest for women who lived in U.S. regions of high solar radiation and little or no reduction was found for women who lived in regions of low solar radiation.47 The data are in keeping with experimental results suggesting that high amounts of vitamin D and dietary Ca decrease susceptibility to chemically induced breast cancer.48
Prostate cancer is the most commonly diagnosed and the second most fatal cancer in American men. The inverse correlation between the mortality rate from prostate cancer and exposure to UV radiation in the U.S. population indicates that one precipitating factor for prostate cancer might be vitamin D deficiency.49 The biochemical evidence to support a role for vitamin D in prostate cancer includes the following: the abundant presence in prostate cells of vitamin D receptors, which show a special affinity for calcitriol, the active form of vitamin D; the antiproliferative, apoptotic, and prodifferentiation activities of calcitriol and its analogs in prostate cells50,51; and the presence in prostate cells of the enzyme 1¸-OHase, which converts calcidiol to calcitriol.52 The hypothesis of a vitamin D dependency for prostate cancer has recently been confirmed by a large, nested, case-control study.53 In this 13-year follow-up study of about 19,000 middle-aged Finnish men, prostate cancer risk was highest among the group of younger men (ages 40 to 51 years) who had low serum calcidiol levels. Low calcidiol levels, however, appeared not to increase prostate cancer risk in older men (> 51 years). According to the authors, the data indicate that vitamin D has a protective role against prostate cancer only before the andropause, when serum androgen levels are higher. Furthermore, the lowest calcidiol concentrations in the younger men were associated with more aggressive prostate cancer.
UV radiation and skin cancer: Skin cancer is the most common cancer in the U.S., with about 1.3 million new cases diagnosed every year. It accounts for nearly 8,000 deaths annually, which represents about 2% of all cancer deaths.54 There are three major types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. Although they have the lowest incidence, melanomas account for nearly 80% of all skin cancer deaths (see
www.cancer.gov). Mortality from melanoma increased dramatically after the 1970s but has declined slightly in the late 1990s, possibly reflecting increased prevention and/or early detection practices. Since the late 1940s, the medical profession has stressed to the public the role of sunlight, especially of UV radiation, in the etiology of skin cancer, and provided certain loose guidelines to follow in reducing the harmful rays of the sun, namely, to stay out of the sun between 10 am to 3 pm if at all possible, but if it does become necessary to go outside, then to use a sunscreen of SPF 15 or higher; to always cover up exposed skin; to make sure to never burn; and to take extra care with children. Despite the known risks of UV exposure and attempts by health care professionals to educate the public, sunbathing and indoor tanning have remained tenaciously popular. Today, excessive UV exposure is recognized as the major cause of the approximately 1.3 million new cases of skin cancer diagnosed in the U.S. each year.
Risks versus benefits of UV radiation: The mounting scientific evidence that insufficient exposure to sunlight and subsequent deficiency of vitamin D and loss of its health benefits are prompting widespread comment, both in the scientific and professional literature and in the media.55-57 To quote one of the sources, "Government advice to 'cover up, keep in the shade … and use factor 15 plus sunscreen' is based on outdated information, mistaken interpretation of evidence and guesswork. It ignores evidence showing that insufficient vitamin D is closely associated with, and almost certainly is a cause of, dozens of chronic diseases including 16 different types of cancers, several nervous system diseases including schizophrenia and multiple sclerosis, diabetes, raised blood pressure, polycystic ovary disease, menstrual problems, infertility, infections and dental decay."54
It is also the contention of many vitamin D and Ca experts that mortality from low vitamin D is far greater than from UV-induced skin cancer. According to Grant, over 20,000 Americans die prematurely annually from insufficient vitamin D synthesized via UV-B alone, compared to only about 8,000 from skin cancer.58
Safety and Toxicity
To date, there are no credible reports of vitamin D toxicity in healthy adults after intensive sunlight exposure.15 In general, vitamin D in the skin reaches a plateau after only 15 to 60 minutes of UV-B exposure. After that, vitamin D~inactive substances such as lumisterol and tachysterol are produced, which are not absorbed into the systemic circulation. Thus, the maximum calcidiol level corresponding to an intensive UV-B exposure is considered by some as an upper limit (UL) of safety (~ 200 nmol/L) for the vitamin.15
In reviews of over 30 well-documented studies, it was found that calcidiol levels in all cases of vitamin D intoxication were well above 200 nmol/L.59-61 Levels up to 1,000 nmol/L were observed. In all cases, toxicity was the result of an excessive oral intake of vitamin D2 or vitamin D3, which then underwent hepatic 25-hydroxylation leading to high circulating calcidiol levels and, hence, hypercalcemia. Hypercalcemia, the major adverse effect of vitamin D intoxication, results primarily from intestinal Ca hyperabsorption and, to a lesser degree, from Ca release from bone62 mediated by calcidiol and/or calcitriol, although which of the two is the main signaling molecule causing vitamin D toxicity remains a point of contention.61
A tolerable upper intake level or no observed adverse effect level (NOAEL), as defined by FNB, is especially difficult for vitamin D. The concentration referred to must be that for circulating calcidiol because of the uncertain amount of the environmental component (dietary or solar). Another factor is that some individuals show hypersensitivity to vitamin D, which most commonly manifests itself as hyperparathyroidism. FNB has defined a NOAEL of 25 mcg (100 IU) vitamin D/day for infants and 50 (200 IU) mcg/day for children older than 1 year and for adults.7
The rationale for the threshold of 25 mcg/day in infants is not well founded, as most documented cases of intoxication occurred in children when circulating calcidiol could not be measured. Furthermore, recent observations suggest that an oral vitamin D intake of up to 100 mcg (400 IU)/day is safe in the adult population. No changes in serum and urinary Ca levels were obtained. The largest calcidiol level after administration of 100 mcg vitamin D/day was 140 nmol/L, which was in the range also seen during intensive UV-B exposure.63
Dealing With Insufficiency
While there is a possibility of vitamin D insufficiency, even deficiency, in the whole population during winter, it is the elderly and institutionalized persons who are at greatest risk throughout the year. Decreased availability of vitamin D may be dealt with by prevention and/or treatment. However, because vitamin D may be derived from two separate sources, from sunlight or diet, the strategy to be employed may need to be individualized for different subjects and changing circumstances. Accurate estimates of vitamin D intakes in the U.S. are not available, in part because the vitamin D composition of fortified foods is highly variable and not properly surveyed and exposure to sunlight is not uniform.
Available modes of prevention and/or treatment are threefold: dermal vitamin D application, enhanced exposure to UV-B light, and increased oral vitamin D intake.15 Dermal application of a vitamin D ointment over several weeks, as with estrogens, might prove to be one way to remedy the insufficiency. However, there are no reported clinical trials to indicate that this measure is effective.
Greater exposure to sunlight during winter may not prove to be effective due to the lack of adequate UV-B radiation. Moreover, there are serious concerns of skin cancer and photoageing of the skin on prolonged sunlight exposure that might be necessary to access enough UV-B rays. While use of artificial UV light is a possibility, the available devices, like tanning beds and sunlamps, are unacceptable as a means of getting the daily dose of vitamin D because they provide high levels of UV-A and very little of UV-B. Sunlamps which provide a natural balance of the two rays are available (e.g., from Sperti Sunlamps,
www.sperti.com). When UV rays from fluorescent lamps were provided to the institutionalized and the elderly, the results were inconsistent, and complications such as skin burns, keratoconjunctivitis, and cataracts were observed.63 However, adverse effects associated with sun exposure may be avoided by frequent sunbathing in low-level radiation for short periods of time and without sunscreen to maximize the benefits. Adequate UV-B exposure and vitamin D production can be achieved in less time than it takes to cause skin redness, burning, tanning, and skin cancer~causing effects of UV radiation.
Daily oral intake of vitamin D may be an easy and effective way to maintain an adequate physiological status of the vitamin. However, the sun-mediated synthesis of vitamin D in the skin is profoundly affected by a wide range of factors, including degree of skin pigmentation, latitude, time of day, season of the year, weather conditions, and the amount of body surface that is covered with clothing or sunscreen. Thus it becomes difficult to estimate an average daily intake to subsidize the solar component. Furthermore, only a few foods contain significant amounts of vitamin D (TABLE 1). After vitamin D was recognized as being critically important for prevention of rickets, the U.S., Canada, and many other countries instituted a policy of fortifying some foods with the vitamin. Milk was chosen as the principal dietary component to be fortified, and others, like breakfast cereals, margarine, and bread, were subsequently included. However, surveys in the 1990s found that up to 70% of milk sampled in the U.S. and Canada contained less vitamin D than the prevailing labeling standards of 8 to 12 mcg (320~480 IU)/quart. Proprietary infant formulas must also contain vitamin D in the amount of 10 mcg (400 IU)/liter. However, these products have also been found to have wide variability in their vitamin D content.7
According to one source, the Recommended Daily Allowance for vitamin D is 5 to 10 mcg (200~400 IU)/day and arises from the fact that this amount will prevent rickets in children.61 The FNB, on the other hand, has made recommendations for Adequate Intake for different age-groups: 4.5 mcg (180 IU)/day for children and young adults up to age 18 years; 5.0 mcg (200 IU)/day for 19- to 50-year-olds; 10 mcg (400 IU)/day for 51- to 70-year-olds; and 10 to 20 mcg (400~800 IU)/day for persons older than 70 years.7
A UL of safety has been set at 2,000 IU of vitamin D from all sources. However, vitamin D experts almost unanimously agree that this value is too low.10,11,61,62 Vieth suggests that critical toxicity may occur at doses 10 times larger than this (20,000 IU daily) and that the UL of safety should be set at 10,000 IU,62 while Heaney10 contends that humans use between 3,000 and 5,000 IU of vitamin D a day, about 10 times the FNB recommendations, and has called for upward revisions of these recommendations. However, Chesney is of the opinion that long-term supplementation does not need to be greater than 4,000 IU, especially when combined with UV-B exposure.61
Because of the difficulty in determining the overall vitamin D dietary intake, the extent of absorption from the gut, and production in the body, the Weston A. Price Foundation for Vitamin Research11 and others2,10 have suggested that the following blood levels of the vitamin, reported in terms of calcidiol, would provide a much better indication of its status in the individual: optimal values of 40 to 50 ng/mL, acceptable values of 35 to 55 ng/mL, with levels above 55 ng/mL to be considered toxic to some individuals.
Conclusion
While the major role of vitamin D is in the maintenance of Ca homeostasis, a large body of recent evidence indicates that suboptimal levels of the vitamin contribute to the development of various chronic diseases. Replenishment from various sources readily and effectively alleviates most of the disorders. However, most vitamin D experts are of the opinion that, in general, the medical profession has not fully appreciated the full role of the vitamin in the maintenance of good health.2,6,10,15 Also, since a very convenient and effective source of vitamin D is through sun-mediated synthesis in the skin, and UV radiation is instrumental in many cases of skin cancer, there has been some reluctance on the part of health care professionals to fully address the importance of UV radiation in maintaining good health. There are experts, however, who feel that the evidence for the positive clinical role of vitamin D is so compelling that the FDA should act immediately to revise upward the regulatory guideline values and institute fortification of many more items in the food chain and increase the level of the existing items. They also contend that the official policy should advocate a proper balance between utilizing the cheap and readily available benefits of appropriate exposure to the sun to access much needed vitamin D and restraint from excessive sunbathing in an effort to safeguard against increased incidence of skin cancer.
Editors' Note: The first part of this article is available on the U.S. Pharmacist Web site (
www.uspharmacist.com).
To comment on this article, contact editor~uspharmacist.com.
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Vol. No: 29:12 Posted: 12/15/04
October 2005