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Summary Of Vitamin D Research

These are speaker notes and supporting research for topics discussed at the 3-hour 10/10/09 YOU Meeting.  Other research discussed is listed here.

The Role of Vitamin D

It plays a much larger role in regulating health, than simply promising strong bones. Researchers from around the globe have discovered that getting the recommended daily vitamin D intake could help reduce plaguing health risks such as MS and diabetes.

Ordinarily, a vitamin is an essential element the body cannot create on its own; however, it is possible for people to create all the vitamin D they need from a cholesterol-like precursor.

For adults, the minimum amount of international units (IU) of vitamin D per day should be between 200 to 1,000 IU, though most people don’t even come close to that. For health purposes up to 2,000-5,000 iu is considered safe, but some experts allow up to 10,000 iu.  Women concerned about bone health should take 2,000 iu per day or more. 5,000 is needed in many people to get the full benefits against cancer.  Blood tests are the best way to find out your blood levels, which vary quite a bit.

During the summer months that goal is easily reached, as the human body can generate up to 12,000 IU of vitamin D from only half an hour of sun exposure. However, during winter months, the daily intake people derive from food and sun exposure falls way below the recommended amount. Further, people who live farther from the equator find it extremely difficult to get enough sun to maintain sufficient blood concentrations of the vitamin.

Tidbits

By running tests, researchers attempted to discover the myriad of benefits vitamin D has to offer.

They found that the vitamin helps regulate cell growth, immunity and energy metabolism. It also could possibly serve as a model for drugs that might tame a range of stubborn, hard to treat diseases.

Deficiency Symptoms

One common concern linked to not getting enough vitamin D is leg weakness. According to studies, people who had higher readings of vitamin D also had greater thigh strength. Researchers conducted deficiency studies and found that with a daily vitamin D intake of at least 400 IU, a woman’s risk of being injured in a fall was decreased by 20 percent.

Another group of researchers who linked vitamin D to immune benefits found that subjects given the lowest amount of vitamin D intake were 25 percent more likely to experience tooth-gum detachment than subjects given the highest intake of the vitamin.

 

Vitamin D May Also Prevent Flu

Research Summary

In 1981, R. Edgar Hope-Simpson proposed that a ‘ seasonal stimulus ’ intimately associated with solar radiation explained the remarkable seasonality of epidemic influenza. Solar radiation triggers robust seasonal vitamin D production in the skin ; vitamin D deficiency is common in the winter, and activated vitamin D, 1,25(OH)2D, a steroid hormone, has profound effects on human immunity. 1,25(OH)2D acts as an immune system modulator, preventing excessive expression of inflammatory cytokines and increasing the ‘ oxidative burst ’ potential of macrophages.

Perhaps most importantly, it dramatically stimulates the expression of potent anti-microbial peptides, which exist in neutrophils, monocytes, natural killer cells, and in epithelial cells lining the respiratory tract where they play a major role in protecting the lung from infection. Volunteers inoculated with live attenuated influenza virus are more likely to develop fever and serological evidence of an immune response in the winter.

Vitamin D deficiency predisposes children to respiratory infections. Ultraviolet radiation (either from artificial sources or from sunlight) reduces the incidence of viral respiratory infections, as does cod liver oil (which contains vitamin D). An interventional study showed that vitamin D reduces the incidence of respiratory infections in children. We conclude that vitamin D, or lack of it, may be Hope-Simpson’s ‘ seasonal stimulus ’.

Vitamin D can Even Lower Blood Pressure

Vitamin D can  lower blood pressure in the same way as ACE inhibitors by reducing renin production which in turn reduces angiontensin II. It usually takes 2-3 months for these changes to be seen, and up to six months for full results.

And It Can Improve Your Mental Function

Vitamin D Deficiency Linked to Low Mood State and Lowered Intellectual Ability in Elderly

Abstracted by Susan Sweeny Johnson, PhD, Biochem., December 13, 2006, from Wilkins, Consuelo H. M.D.; Sheline, Yvette I. M.D.; Roe, Catherine M. Ph.D.; Birge, Stanley J. M.D.; Morris, John C. M.D..  Vitamin D Deficiency Is Associated With Low Mood and Worse Cognitive Performance in Older Adults.  Am J Geriatric Psych 14(12):1032-40. December 2006.

Vitamin D deficiency is present in 25-58% of adults over 60.1  This is largely due to a decreased ability to make vitamin D in the skin and to use it in the body.2  Although the correlation of vitamin D with bone density is well established, more recent attention has been paid to the connection between vitamin D and brain function.

Early studies found no correlation of blood concentrations of the vitamin D metabolite, 1,25-dihydroxyvitamin D, with mood disorders, specifically Seasonal Affective Disorder (SAD).3  SAD is a documented syndrome where people tend to get depressed in the winter due to less sunlight exposure. Later studies, however, have shown that lower levels of 25-hydroxyvitamin D, a more stable metabolite, do correlate with SAD.4  SAD responds better to Vitamin D supplementation than to sunlight exposure in some studies.5

Interestingly, other studies have shown a correlation between higher blood vitamin D levels and better muscle control and fewer falls in the elderly.6

In a recent study, 80 adults with an average age of 75 years were selected to participate.  Half of the participants had very mild Alzheimer’s symptoms where brain function was only mildly decreased and half had normal brain function.  Subjects were divided into three subgroups based on vitamin D level as defined by previously reported data : vitamin D-sufficient (serum level of 25-hydroxyvitamin D of greater than or equal to 20 ng/mL), vitamin D-insufficient (serum 25-hydroxyvitamin D of 10–19.9 ng/mL), and vitamin D-deficient (serum 25-hydroxyvitamin D of less than 10 ng/mL).

All participants were tested using a battery of brain function tests, a mood disorder test, and a muscle control and coordination test. The blood concentration of vitamin D as 25-hydroxyvitamin D was determined only once for each participant.

The results indicate a significant relationship between insufficient vitamin D blood concentrations and mood disorders in elderly people. The score on the mood test correlated with the vitamin D concentration group in a statistically significant manner.  The lower the levels of serum 25-hydroxyvitamin D, the lower the scores on the mood test. 

Study participants with lower vitamin D levels also performed significantly lower on two of four brain function tests.  No correlation of vitamin D levels with muscle control was seen in this study.

Vitamin D supplementation in elderly people may be beneficial in enhancing mood and maintaining brain function. However further, larger studies should be done to more carefully measure blood vitamin D levels over a longer period of time.

Reference:

1  Gloth FM, Gundberg CM, Hollis BW, et al: Vitamin D deficiency in homebound elderly persons. JAMA 1995; 274:1683–1686

2  Parfitt AM, Chir B, Gallagher JC, et al: Vitamin D and bone health in the elderly. Am J Clin Nutr 1982; 36:1014–1031

3  Oren DA, Schulkin J, Rosenthal NE:1,25 (OH)2 vitamin D3 levels in seasonal affective disorder: effects of light. Psychopharmacology 1994;116:515–516

4  Kenny AM, Biskup B, Robbins B, et al: Effects of vitamin D supplementation on strength, physical function, and health perception in older, community-dwelling men. J Am Geriatr Soc 2003; 51:1762–1767

5  Gloth FM 3rd, Alam W, Hollis B: Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder. J Nutr Health Aging 1999; 3:5–7

6  Bischoff HA, Staehelin HB, Dick W, et al: Effects of vitamin D and calcium supplementation on falls: a randomized controlled trial. J Bone Miner Res 2003; 18:343–351

 

Experts Reassess Upper Limit of Vitamin D Intake

No Side Effects at 10,000 I.U. Per Day

Abstracted by Susan Sweeny Johnson, PhD, Biochem, January 17, 2007 from John N Hathcock, Andrew Shao, Reinhold Vieth, and Robert Heaney. Risk assessment for vitamin D.  Am J Clin Nutr 2007;85:6 –18.

Vitamin D plays a crucial role in dietary calcium absorption and maintenance of blood calcium levels, both of which have a direct effect on bone health.  Recent studies show that vitamin D may help prevent colon cancer1 and diabetes2 among other things.3

The Food and Nutrition Board’s (FMB’s) current upper limit of vitamin D3 of 50 ìg per day (2000 IU) was calculated based on 10-year old data.  Researchers reviewed the most recent vitamin D studies to determine if the current upper limit should be raised in order to get the most benefit out of vitamin D supplementation.

In order to do this, they compared the results of more than 20 individual studies involving vitamin D3 supplementation.  They gave preference to studies where the amount of vitamin D3 supplementation was correlated with 25-hydroxyvitamin D and calcium blood concentrations.  Hypercalcemia, measured by elevated blood calcium, was selected as the measure of vitamin D toxicity. Hypercalcemia’s clinical manifestations include pain, conjunctivitis, anorexia, fever, chills, thirst, vomiting, and weight loss.

The researchers recommended raising the upper limit for vitamin D supplementation to 250ìg per day (10,000 IU).  At this supplementation level, blood calcium is not elevated.  In fact, over 1200ìg per day is necessary to achieve hypercalcemia. Sunlight exposure, which causes vitamin D to be made in the skin, and any dietary intake from food provide only about 125ìg per day and 10 ìg per day maximum, respectively.  The researchers felt that further studies that included a diverse, large population and used a dose dependent vitamin D supplementation vs. 25-hydroxyvitamin D and calcium blood concentration protocol could raise this upper limit even higher.

It should be noted that the researchers concluded that other possible side effects of vitamin D supplementation, i.e. kidney stones and cardiovascular disease, were not a problem at this level.

Reference:

1  Giovannucci E, Liu Y, Rimm EB, et al. Prospective study of predictors of vitamin D status and cancer incidence and mortality in men. J Natl Cancer Inst 2006;98:451–9

2  Liu S, Song Y, Ford ES, Manson JE, Buring JE, Ridker PM. Dietary calcium, vitamin D, and the prevalence of metabolic syndrome in middle-aged and older U.S. women. Diabetes Care 2005;28:2926 –32

3  Holick MF. High prevalence of vitaminD inadequacy and implications for health. Mayo Clin Proc 2006;81:353–73

 

Vitamin D Casts Cancer Prevention In New Light

Martin Mittelstaedt - From Saturday's Globe and Mail - April 28, 2007 at 1:20 AM EDT

For decades, researchers have puzzled over why rich northern countries have cancer rates many times higher than those in developing countries — and many have laid the blame on dangerous pollutants spewed out by industry.

But research into vitamin D is suggesting both a plausible answer to this medical puzzle and a heretical notion: that cancers and other disorders in rich countries aren't caused mainly by pollutants but by a vitamin deficiency known to be less acute or even non-existent in poor nations.

Those trying to brand contaminants as the key factor behind cancer in the West are "looking for a bogeyman that doesn't exist," argues Reinhold Vieth, professor at the Department of Nutritional Sciences at the University of Toronto and one of the world's top vitamin D experts. Instead, he says, the critical factor "is more likely a lack of vitamin D."

What's more, researchers are linking low vitamin D status to a host of other serious ailments, including multiple sclerosis, juvenile diabetes, influenza, osteoporosis and bone fractures among the elderly.

The main way humans achieve healthy levels of vitamin D is not through diet but through sun exposure. (Eliseo Fernandez/Reuters)

Not everyone is willing to jump on the vitamin D bandwagon just yet. Smoking and some pollutants, such as benzene and asbestos, irrefutably cause many cancers.

But perhaps the biggest bombshell about vitamin D's effects is about to go off. In June, U.S. researchers will announce the first direct link between cancer prevention and the sunshine vitamin. Their results are nothing short of astounding.

A four-year clinical trial involving 1,200 women found those taking the vitamin had about a 60-per-cent reduction in cancer incidence, compared with those who didn't take it, a drop so large — twice the impact on cancer attributed to smoking — it almost looks like a typographical error.

And in an era of pricey medical advances, the reduction seems even more remarkable because it was achieved with an over-the-counter supplement costing pennies a day.

One of the researchers who made the discovery, professor of medicine Robert Heaney of Creighton University in Nebraska, says vitamin D deficiency is showing up in so many illnesses besides cancer that nearly all disease figures in Canada and the U.S. will need to be re-evaluated. "We don't really know what the status of chronic disease is in the North American population," he said, "until we normalize vitamin D status."

 

The Sunshine Vitamin

For decades, vitamin D has been the Rodney Dangerfield of the supplement world. It's the vitamin most Canadians never give a second thought to because it was assumed the only thing it did was prevent childhood rickets, a debilitating bone disease. But the days of no respect could be numbered. If vitamin D deficiency becomes accepted as the major cause of cancer and other serious illnesses, it will ignite the medical equivalent of a five-alarm blaze on the Canadian health front.

For many reasons, Canadians are among the people most at risk of not having enough vitamin D. This is due to a quirk of geography, to modern lifestyles and to the country's health authorities, who have unwittingly, if with the best of intentions, played a role in creating the vitamin deficiency.

Authorities are implicated because the main way humans achieve healthy levels of vitamin D isn't through diet but through sun exposure. People make vitamin D whenever naked skin is exposed to bright sunshine. By an unfortunate coincidence, the strong sunshine able to produce vitamin D is the same ultraviolet B light that can also causes sunburns and, eventually, skin cancer.

Only brief full-body exposures to bright summer sunshine — of 10 or 15 minutes a day — are needed to make high amounts of the vitamin. But most authorities, including Health Canada, have urged a total avoidance of strong sunlight or, alternatively, heavy use of sunscreen. Both recommendations will block almost all vitamin D synthesis.

Those studying the vitamin say the hide-from-sunlight advice has amounted to the health equivalent of a foolish poker trade. Anyone practising sun avoidance has traded the benefit of a reduced risk of skin cancer — which is easy to detect and treat and seldom fatal — for an increased risk of the scary, high-body-count cancers, such as breast, prostate and colon, that appear linked to vitamin D shortages.

The sun advice has been misguided information "of just breathtaking proportions," said John Cannell, head of the Vitamin D Council, a non-profit, California-based organization.

"Fifteen hundred Americans die every year from [skin cancers]. Fifteen hundred Americans die every day from the serious cancers."

Health Canada denies its advice might be dangerous. In an e-mailed statement, it said that most people don't apply sunscreen thoroughly, leaving some skin exposed, and that people spend enough time outside without skin protection to make adequate amounts of vitamin D.

However, the Canadian Cancer Society last year quietly tweaked its recommendation to recognize that limited amounts of sun exposure are essential for vitamin D levels.

Avoiding most bright sunlight wouldn't be so serious if it weren't for a second factor: The main determinant of whether sunshine is strong enough to make vitamin D is latitude. Living in the north is bad, the south is better, and near the equator is best of all.

Canadians have drawn the short straw on the world's latitude lottery: From October to March, sunlight is too feeble for vitamin D production. During this time, our bodies draw down stores built by summer sunshine, and whatever is acquired from supplements or diet.

Government regulations require foods such as milk and margarine to have small amounts of added vitamin D to prevent rickets.

Other foods, such as salmon, naturally contain some, as does the cod liver oil once commonly given to children in the days before milk fortification. But the amounts from food are minuscule compared to what is needed for cancer prevention and what humans naturally can make in their skin.

Vitamin D levels in Canada are also being compromised by a lifestyle change. Unlike previous generations that farmed or otherwise worked outside, most people now spend little time outdoors.

One survey published in 2001 estimated office- and homebound Canadians and Americans spend 93 per cent of waking time in buildings or cars, both of which block ultraviolet light.

Consequently, by mid-winter most Canadians have depleted vitamin D status. "We're all a bit abnormal in terms of our vitamin D," said Dr. Vieth, who has tested scores of Canadians, something done with a simple blood test.

 

How Much Is Enough?

Just how much vitamin D is required for optimum health is the subject of intense scientific inquiry.

Dr. Vieth has approached the matter by asking: What vitamin D level would humans have if they were still living outside, in the wild, near the equator, with its attendant year-round bright sunshine? "Picture the natural human as a nudist in environments south of Florida," he says.

He estimates humans in a state of nature probably had about 125 to 150 nanomoles/litre of vitamin D in their blood all year long — levels now achieved for only a few months a year by the minority of adult Canadians who spend a lot of time in the sun, such as lifeguards or farmers.

For the rest of the population, vitamin D levels tend to be lower, and crash in winter. In testing office workers in Toronto in winter, Dr. Vieth found the average was only about 40 nanomoles/L, or about one-quarter to one-third of what humans would have in the wild.

The avalanche of surprising research on the beneficial effects of vitamin D could affect dietary recommendations as well. Health Canada says that, in light of the findings, it intends to study whether recommended dietary levels need to be revised, although the review is likely to be years away.

A joint Canadian-U.S. health panel last studied vitamin D levels in 1997, concluding the relatively low amounts in people's blood were normal. At the time, there was speculation vitamin D had an anti-cancer effect, but more conclusive evidence has only emerged since.

"There needs to be a comprehensive review undertaken and that is planned," says Mary Bush, director general of Health Canada's office of nutrition policy and promotion.

But Ms. Bush said the government doesn't want to move hastily, out of concern that there may be unknown risks associated with taking more of the vitamin.

Those who worry about low vitamin D, however, say this stand is too conservative — that the government's caution may itself be a health hazard.

To achieve the vitamin D doses used for cancer prevention through foods, people would need to drink about three litres of milk a day, which is unrealistic.

If health authorities accept the new research, they would have to order a substantial increase in food fortification or supplement-taking to affect disease trends. As it is, the 400 IU dosage included in most multivitamins is too low to be an effective cancer fighter.

Dr. Vieth said any new recommendations will also have to reflect the racial and cultural factors connected to vitamin D. Blacks, South Asians and women who wear veils are at far higher risks of vitamin D deficiencies than are whites.

Although humans carry a lot of cultural baggage on the subject of skin hue, colour is the way nature dealt with the vagaries of high or low vitamin D production by latitude.

Those with very dark skins, whose ancestors originated in tropical, light-rich environments, have pigmentation that filters out more of the sunshine responsible for vitamin D; in northern latitudes, they need more sun exposure — often 10 times as much — to produce the same amount of the vitamin as whites.

Dr. Vieth says it is urgent to provide information about the need for extra vitamin D in Canada's growing non-white population to avoid a future of high illness rates in this group.

Researchers suspect vitamin D plays such a crucial role in diseases as unrelated as cancer and osteoporosis because the chemical originated in the early days of animal evolution as a way for cells to signal that they were being exposed to daylight.

Even though living things have evolved since then, almost all cells, even those deep in our bodies, have kept this primitive light-signalling system.

In the body, vitamin D is converted into a steroid hormone, and genes responding to it play a crucial role in fixing damaged cells and maintaining good cell health. "There is no better anti-cancer agent than activated vitamin D. I mean, it does everything you'd want," said Dr. Cannell of the Vitamin D Council.

Some may view the sunshine-vitamin story as too good to be true, particularly given that the number of previous claims of vitamin cure-alls that subsequently flopped. "The floor of modern medicine is littered with the claims of vitamins that didn't turn out," Dr. Cannell allowed.

But the big difference is that vitamin D, unlike other vitamins, is turned into a hormone, making it far more biologically active. As well, it is "operating independently in hundreds of tissues in your body," Dr. Cannell said.

Referring to Linus Pauling, the famous U.S. advocate of vitamin C use as a cure for many illnesses, he said: "Basically, Linus Pauling was right, but he was off by one letter."

 

Framingham Researchers Find Heart Disease Linked To Vitamin D Deficiency

A report published in the January 8, 2007 issue of Circulation: A Journal of the American Heart Association revealed the discovery of Framingham Heart Study researchers that having deficient levels of vitamin D is associated with double the risk of experiencing a cardiovascular event, including heart attack, heart failure or stroke, within a five year period compared to individuals with normal levels.

For the current study, Harvard Medical School assistant professor of medicine Thomas J. Wang, MD and colleagues evaluated data from 1,739 offspring of Framingham Heart Study participants. The subjects, whose average age was 59 and who had no evidence of cardiovascular disease upon enrollment, were tested for serum vitamin D levels and followed for an average of 5.4 years, during which they received periodic physical examinations and lab assessments of cardiovascular risk factors.

Evaluation of vitamin D concentrations found that only 10 percent of the participants had optimal levels of over 30 nanograms per milliliter. Twenty-eight percent were found to have levels that were less than half the optimal level, and 9 percent had concentrations lower than 10 ng/mL. Analysis of the data determined that having deficient blood levels of vitamin D at below 15 nanograms per milliliter doubled the risk of having a cardiovascular event over follow up, compared to those with normal levels. After adjustment for conventional cardiovascular risk factors, the risk remained 62 percent higher than that experienced by non-deficient individuals.

In a separate analysis of 688 of the participants, hypertension was found to double event risk among vitamin D deficient individuals after adjustment for traditional cardiovascular risk factors. “Vitamin D deficiency is associated with increased cardiovascular risk, above and beyond established cardiovascular risk factors,” Dr Wang stated. “The higher risk associated with vitamin D deficiency was particularly evident among individuals with high blood pressure.”

“Low levels of vitamin D are highly prevalent in the United States, especially in areas without much sunshine,” he observed. “Twenty to 30 percent of the population in many areas has moderate to severe vitamin D deficiency.”

“A growing body of evidence suggests that low levels of vitamin D may adversely affect the cardiovascular system,” he continued. “Vitamin D receptors have a broad tissue distribution that includes vascular smooth muscle and endothelium, the inner lining of the body’s vessels. Our data raise the possibility that treating vitamin D deficiency, via supplementation or lifestyle measures, could reduce cardiovascular risk.”

 

Higher Vitamin D Levels Associated With Speedier Brain Processing

In an article published on May 21, 2009 online in the Journal of Neurology, Neurosurgery and Psychiatry, European researchers report that men with higher vitamin D levels performed better on a test of attention and speed of information processing than those with lower levels of the vitamin.

Dr David M. Lee of the University of Manchester's School of Translational Medicine and his associates administered 3 tests of cognitive function to 3,369 men aged 40 to 79 from 8 centers participating in the European Male Aging Study (EMAS). Fasting blood samples collected from the subjects were analyzed for serum 25-hydroxyvitamin D levels.

Men whose vitamin D levels were higher were found to perform better on all three tests, although the Digit Symbol Substitution test, which measures psychomotor speed and visual scanning, was the only test whose scores were associated with vitamin D levels after adjustment for several factors. Further analysis revealed that higher test scores were particularly associated with increased vitamin D levels in older men.

Although the authors write that the mechanisms of vitamin D in cerebral functions are unknown, they note that vitamin D has been shown to increase choline acetyltransferase activity in rat brains and that there is also evidence that the vitamin provides a neuroprotective effect. Furthermore, parathyroid hormone and calcium levels, which are affected by vitamin D, could be involved in cognitive function. Additionally, low serum vitamin D levels have been associated with a greater risk of depression, and higher levels of vitamin D were found to be associated with lower depression scores in the current study.

“Previous studies exploring the relationship between vitamin D and cognitive performance in adults have produced inconsistent findings but we observed a significant, independent association between slower information processing speed and lower levels of vitamin D,” stated Dr Lee. “The main strengths of our study are that it is based on a large population sample and took into account potential interfering factors, such as depression, season and levels of physical activity.

“Interestingly, the association between increased vitamin D and faster information processing was more significant in men aged over 60 years, although the biological reasons for this remain unclear," he added. “The positive effects vitamin D appears to have on the brain need to be explored further but certainly raise questions about its potential benefit for minimizing age-related declines in cognitive performance. "

"If cognitive function can be improved by a simple intervention such as vitamin D supplementation, this would have potentially important implications for population health," the authors conclude. "In light of our findings, and the fact that vitamin D inadequacy is common among adults, further prospective studies are warranted to determine whether vitamin D supplementation could aid in minimizing aging-related declines in specific cognitive domains.

  *    *    *

In the following trial, supplementation with modest amounts of vitamin D, plus calcium, resulted in a 77% reduction in the incidence of all cancers over the following 4 years. Not a typo… 77% less cancer of all types.

Vitamin D And Calcium Supplementation Reduces Cancer Risk:

Results Of a Randomized Trial 1, 2

Joan M Lappe, Dianne Travers-Gustafson, K Michael Davies, Robert R Recker, and Robert P Heaney

ABSTRACT

Background: Numerous observational studies have found supple- mental calcium and vitamin D to be associated with reduced risk of common cancers. However, interventional studies to test this effect are lacking.

Objective: The purpose of this analysis was to determine the efficacy of calcium alone and calcium plus vitamin D in reducing inci- dent cancer risk of all types.

Design: This was a 4-y, population-based, double-blind, randomized placebo-controlled trial. The primary outcome was fracture incidence, and the principal secondary outcome was cancer inci- dence. The subjects were 1179 community-dwelling women ran- domly selected from the population of healthy postmenopausal women aged ��55 y in a 9-county rural area of Nebraska centered at latitude 41.4°N. Subjects were randomly assigned to receive 1400 – 1500 mg supplemental calcium/d alone (Ca-only), supplemental calcium plus 1100 IU vitamin D3/d (Ca �� D), or placebo.

Results: When analyzed by intention to treat, cancer incidence was lower in the Ca �� D women than in the placebo control subjects (P �� 0.03). With the use of logistic regression, the unadjusted relative risks (RR) of incident cancer in the Ca �� D and Ca-only groups were 0.402 (P �� 0.01) and 0.532 (P �� 0.06), respectively. When analysis was confined to cancers diagnosed after the first 12 mo, RR for the Ca �� D group fell to 0.232 (CI: 0.09, 0.60; P �� 0.005) but did not change significantly for the Ca-only group. In multiple logistic regression models, both treatment and serum 25-hydroxyvitamin D concentrations were significant, independent predictors of cancer risk.

Conclusions: Improving calcium and vitamin D nutritional status sub- stantially reduces all-cancer risk in postmenopausal women. This trial was registered at clinicaltrials.gov as NCT00352170. Am J Clin Nutr 2007;85:1586 –91.

This seeming protection was presumed to be mediated by the effect of solar radiation on vitamin D status. Exploration of the connection between vitamin D nutriture and chronic disease in humans received a critical stimulus with the availability of a physiologically stable indicator of vitamin D status [serum 25- hydroxyvitamin D, or 25(OH)D] and the designation of 25(OH)D as the functional indicator of vitamin D status by the Institute of Medicine (11).

These developments have facilitated a more precise definition of the relation between cancer risk and vitamin D status. The inverse association has now been estab- lished for incident colorectal cancer (12) and for prostate cancer (13), among others. Gorham et al (14), quantifying the inverse relation between serum 25(OH)D and risk of colorectal cancer, calculated a 50% reduction in cancer risk at serum 25(OH)D concentrations ��80 nmol/L.

Giovannucci (15, 16) and Holick (17, 18) have each recently reviewed the now large body of evidence linking low vitamin D status to increased risk of cancer. Similar associations were ear- lier noted for high calcium intake and reduced cancer risk (19 – 21), most prominently for colorectal cancer, whereby a luminal effect of high calcium intake provided a plausible mechanism. The human evidence to date linking cancer and vitamin D has been observational in character, although several of the many positive studies linking vitamin D and cancer have been prospec- tive.

We had the opportunity to examine the relation of these nutrients to cancer incidence in a 4-y, double-blind, placebo- controlled trial of calcium and vitamin D supplementation for which cancer was the principal secondary endpoint. The null hypothesis was that there would be no difference in all-cancer incidence between the 3 calcium and vitamin D treatment groups.

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