TWENTY-FIVE THOUSAND YEARS ago, our Paleolithic ancestors got plenty of sun. Scantily draped in animal hides, they spent their days roaming outdoors, hunting and gathering food. With so much sun exposure, they made a lot of vitamin D, the “sun vitamin,” through their skin—around 10,000 units per day, biologists estimate.
Today, with lifestyles that keep us indoors and in vehicles, we don’t get out in the sun nearly as much. And when we do, we often slather ourselves in sunscreen to avoid skin cancer—a protective measure that unfortunately also blocks production of vitamin D. Although we get vitamin D from our food, primarily through fatty fish and fortified milk, yogurt and cereal, there’s been growing concern over the past decade that we aren’t getting enough, and that we may be missing out on a number of the vitamin’s health benefits that we’re just starting to understand.
And if newspaper headlines are to be believed, we could be missing quite a lot. Week after week, articles are published touting vitamin D’s protective role in a wide range of diseases and ailments—cardiovascular disease, hypertension, cancers of the colon, breast and prostate, cold and flu, asthma, autism, depression, osteoporosis, arthritis, neurodegenerative disease, multiple sclerosis, type I diabetes—and even longevity. But don’t count on all of these studies panning out, warns CALS biochemist Hector DeLuca. DeLuca should know—he’s a globally recognized authority on vitamin D whose six decades of research laid the groundwork for much of what we know and are discovering about it today.
“I’m really worried about how much attention vitamin D has received lately because we did this with vitamin E many years ago—where vitamin E was going to cure all kinds of things and of course it didn’t—and it’s completely off the radar screen now,” DeLuca says. “I don’t want that to happen to vitamin D because there are many places where it’s really effective.”
So what are vitamin D’s health benefits, and what do we need to do to maximize them? Both are huge questions in the scientific and medical fields. At this point, only one thing is certain: vitamin D is essential for strong bones. Beyond that, the jury is out because we don’t have the large, randomized human clinical trials required to make those calls—yet.
Nevertheless, there have been a significant number of promising in vitro and animal studies over the years, enough to convince many vitamin D researchers to increase their own doses. And when the U.S. Institute of Medicine in 2010 raised the Recommended Dietary Allowance for vitamin D from 400 to 600 units per day for adults—taking into consideration only the vitamin’s impact on bone health—it didn’t sit well with many members of the vitamin D research community who think the recommended intake should be considerably higher.
“Many people thought that was absolutely absurd—that people should actually be taking anywhere from 2,000 to 4,000 units a day,” says Wes Pike, another CALS vitamin D researcher who is internationally respected for his work. “But the committee didn’t take any risks. They discounted all the other things that people believe higher amounts of vitamin D could be beneficial for—muscle function, a healthy immune system, combating cancer and so much more. And some of those things are real, it’s just that there’s no strong clinical evidence for them yet.”
Fortunately, there soon will be a lot more solid evidence about vitamin D’s health impacts—on heart disease, stroke, cancer and more—thanks to a large clinical trial that’s gearing up at the Institute of Medicine’s request. As scientists, doctors and the public wait for answers, CALS researchers are working in parallel, leading an equally important effort to shine a light on vitamin D’s mode of action inside the body and to explore and understand new vitamin D-based treatments for disease—as they have for almost a century.
THE STORY OF VITAMIN D is largely a CALS story. It was identified by biochemist Elmer McCollum, who discovered vitamins A and B as a young faculty member at CALS before joining Johns Hopkins University, where in 1921 he found a substance that cured the bone-softening disease rickets—and named it vitamin D, as it was then the fourth vitamin known to science. In 1923 CALS biochemist Harry Steenbock figured out how to biofortify food with vitamin D by exposing it to ultraviolet light, a discovery that led to the almost complete eradication of rickets by the mid-1940s.
As his last graduate student, Steenbock in 1951 brought on Hector DeLuca, a promising young chemist from the University of Colorado. At Steenbock’s request, DeLuca stayed on to run his lab. “Steenbock was nearing retirement and wasn’t physically well, so he asked if I would stay after my Ph.D. and direct the research in his lab,” says DeLuca. The offer turned into a faculty position in 1959.
“At the time there was a lot we didn’t know about vitamin D and how it makes better bones,” says DeLuca. “I thought, ‘Why don’t we try to figure out how it works, and maybe we’ll learn how certain diseases take place?’ That was my motivation.”
And figure it out he did. By administering radioactive vitamin D to animals and then following its path through their bodies, DeLuca discovered that the vitamin D we get from the sun and through our diets isn’t the biologically active form of the compound. In fact, to become activated, it must undergo two sequential changes. First, it’s converted in the liver to calcidiol (25-hydroxyvitamin D3), which is the predominant form that circulates in the blood. Second, this circulating form is converted in the kidneys to calcitriol (1,25-dihydroxyvitamin D3), a steroid hormone.
DeLuca patented these discoveries in 1971, and by 1974 had defined the vitamin D endocrine system—how the body’s organs use vitamin D to maintain steady calcium levels in the blood. When levels drop too low, the kidney produces more calcitriol, signaling to the small intestine to increase calcium absorption from food and to the bones to disperse some of their mineral stores.
Interest in vitamin D grew after this groundbreaking discovery, and a number of labs joined the race to understand the hormone’s mode of action in the body. Two groups—DeLuca’s and one that included Wes Pike—solved the puzzle at essentially the same time in the late 1980s, deciphering the genetic sequence of the receptor molecule for the vitamin D hormone in rats and humans, respectively. It turned out to be an intracellular receptor that, when bound to calcitriol, enters the nucleus and alters gene expression.
“The medical impact of all of this work was enormous. All of the vitamin D-resistant diseases came into focus,” says DeLuca. “Some were due to defects in the enzyme that makes the vitamin D hormone. Others were due to defects in the vitamin D receptor.” DeLuca’s early findings alone led to treatments for vitamin D-resistant rickets, hypoparathyroidism, renal osteodystrophy, drug-induced bone disease and osteoporosis using synthetic calcitriol.
Even before the receptor was cloned, researchers had begun to examine its distribution in the body’s tissues. They found it, as expected, in the intestine, bone and kidney, where it plays a role in the vitamin D endocrine system. But its presence in so many other tissues—including breast, colon, lung, ovary, prostate, parathyroid, the pancreas’ insulin-producing cells and some immune cells—came as a huge surprise, giving scientists their first clue that vitamin D likely plays a much broader role in human health. “That’s when we realized vitamin D has other biological actions in the body,” says DeLuca.
When DeLuca discovered the active hormone form of vitamin D in 1970, he also found more than two dozen other very similar-looking molecules in the body. Although all of these metabolites turned out to be inactive, DeLuca was struck by an idea: to try to build vitamin D-like compounds, or analogs, that could be therapeutically useful.
While the vitamin D hormone itself can be—and is—used to treat a number of diseases, it has severe side effects that limit how much can be administered. That’s because calcitriol levels are tightly regulated by the body. No matter how much vitamin D you get through sun exposure and diet (within reason, of course), the amount of active vitamin D hormone in your system stays about the same. But when patients are given the hormone directly, it bypasses this regulation and tends to increase blood calcium levels, a dangerous condition known as hypercalcemia. But analogs, DeLuca figured, could possibly get around this problem if ones could be found that maximize vitamin D’s effect on desired tissues while minimizing its effect on the small intestine and bone—and thereby reducing hypercalcemia. So, in addition to basic research, DeLuca launched a program to synthesize novel vitamin D analogs and test their properties.
The program has been a stunning success. Over the years, DeLuca’s lab has synthesized more than 800 unique vitamin D hormone analogs, some of them exquisitely tissue-specific. Of his analogs, several have become pharmaceuticals that have impacted the lives of millions of people suffering from osteoporosis, vitamin D-resistant rickets and bone diseases associated with kidney failure. In the latter case, the top two drugs on the market—Zemplar and Hectoral—are DeLuca’s. They replace the vitamin D hormone the patient’s kidneys can no longer make, but with significantly less hypercalcemia.
“These drugs serve almost half a million people on dialysis,” says Paul Kellerman, a nephrologist with the UW–Madison School of Medicine and Public Health and medical director for Wisconsin Dialysis. “And when you take into consideration other people with late-stage kidney disease, you are talking about a patient population that’s probably over a million that needs these medications.”
DeLuca is always looking for the next best thing—the new analog that, because of its slightly altered shape, changes the vitamin D receptor’s conformation to give it even more desirable properties. He believes he may have a new one for dialysis patients he’s calling “2MD.” The compound is a top prospect for Deltanoid Pharmaceuticals, a company DeLuca co-founded in 2000 with his fellow biochemistry professor and wife, Margaret Clagett-Dame, to help develop promising analogs to the point where large pharmaceutical companies will take over. “Each of these compounds for dialysis patients has been an improvement on the one before it—doing a better job of controlling parathyroid hormone production without raising serum calcium,” he says. “That’s the game we’re playing with analogs.”
Through the Wisconsin Alumni Research Foundation (WARF), DeLuca has filed and received more than 1,500 patents on his analogs and other inventions. WARF estimates these patents have earned more than $500 million in royalties over the past 30 years, much of which has gone to fuel UW–Madison’s research engine.
Interestingly, WARF’s very inception rests on CALS’ vitamin D research. Harry Steenbock conceived of founding it as the nation’s first university technology transfer office to collect, invest and distribute money earned through research-based discovery. WARF’s first licensing agreement with Quaker Oats in 1927 led to the fortification of breakfast cereals with vitamin D.
DeLuca, although he formally retired last year at age 81, still has an active lab employing five scientists who synthesize new vitamin D analogs under his direction. He also continues to study vitamin D’s role in immune disease and is screening for analogs that could help protect insulin-producing islet cells—or islet cell transplants—in patients with type I diabetes. “I think type I diabetes is an area where vitamin D can really help,” he says.
About a decade ago, DeLuca was instrumental in recruiting Wes Pike to the UW–Madison campus, a move calculated to ensure the department’s continued leadership in basic vitamin D research.
“At my age, I’m more interested in the medical applications, so that’s the direction my lab has taken,” he says. “Wes is taking the next step at the molecular level.”
ONE COULD say that Wes Pike wrote the book on vitamin D. It’s true—literally. The third edition of Vitamin D, a 2,000-plus-page textbook he co-edited, came out last year. Within the field, Pike’s expertise focuses on how the vitamin D receptor regulates gene expression. Since joining CALS in 2001, he’s established a respected, highly productive lab that interacts regularly with DeLuca’s group.
“We have common research meetings every week and we’ve worked on a number of projects together over the years,” says Pike. “It’s a really good collaboration because without understanding how the basic hormone affects gene regulation, we can’t possibly understand the nuances through which Hector’s analogs work.”
This regulation fascinates Pike because it orchestrates all of vitamin D’s various biological effects in the body. His goal is to understand its intricacies. “We’re interested in where the vitamin D receptor binds to DNA, how it binds and how it actually regulates transcription—what activator proteins and other protein complexes it recruits,” he says. While the vitamin D receptor is believed to regulate around 200 genes, Pike focuses his attention on a key few—those he believes have the greatest therapeutic promise.
One of his targets is the vitamin D receptor gene itself. Without receptors, cells can’t respond to vitamin D. Pike would like to find a way to turn the gene on—or dial it up—where it’s needed. “If we could take a tissue and upregulate the receptor, then we could increase the tissue’s sensitivity to existing levels of the vitamin D hormone. That’s a good thing. That’s a therapeutic possibility,” he says.
Pike also is interested in the RANKL gene, and he’s not the only one. The gene’s protein, also called RANKL, promotes bone resorption and is associated with osteoporosis and weak bones. Pharmaceutical giant Amgen developed an antibody against the RANKL protein—which binds and neutralizes its activity—to treat osteoporosis in post-menopausal women. The drug, known as denosumab, is sold under the trade name Prolia for this purpose, and it also has been approved to prevent fractures caused by cancers that have spread to the bone. Prolia works wonders in preventing bone loss, but there can be problems with antibody treatments.
That’s because many proteins have multiple effects in the body, good and bad. The RANKL protein, for instance, is known to help boost immune function—but the antibody wipes out that activity, too. And a single antibody treatment can last for months. “Once it’s in you, you can’t change anything for four months,” says Pike, who is exploring an alternative treatment approach. If he can learn enough about how the vitamin D receptor regulates RANKL’s expression, he believes he may be able to turn off the RANKL gene specifically where it’s not wanted.
“So rather than allow the cells to make RANKL and then shut the protein down on a global scale—on a total body scale—we want to find a way to shut the gene down at its transcriptional roots, so to speak, in a cell-selective way. We want to turn it down in the skeleton, but not in the immune cells,” says Pike.
To that end, Pike recently set up a sophisticated system to quickly screen for analogs and other compounds that fit the bill. A positive hit could yield a next-generation drug more targeted than Prolia. He’s also found some cell-specific differences in the DNA binding sites that the vitamin D receptor uses to regulate the RANKL gene—information that also could be leveraged in a therapeutic intervention.
AS SCIENTISTS AT CALS and around the globe work to unlock the molecular secrets of vitamin D and develop promising new therapeutic compounds and approaches, a massive clinical trial is under way that should be able to answer—definitively—many of the medical establishment’s most pressing questions about the vitamin’s role in human health and disease. The study, known by the acronym VITAL, will track the health outcomes of 20,000 older men and women for five years as they take either vitamin D (2,000 units per day), fish oil, both supplements or a placebo. The study was designed to monitor for heart disease, stroke and cancers—particularly cancers of the colon, breast and prostate—but the investigators also plan to watch for effects on diabetes, high blood pressure, bone density, vision, memory loss, depression, autoimmune diseases and other conditions.
“In 10 years we’ll know an awful lot more,” says Pike. “I think some of these health effects will be borne out, and by then we’ll have figured out the mechanisms that make vitamin D protective.”
In the meantime, DeLuca offers this advice: “My message is to be sure you get plenty of vitamin D so that you’re vitamin D normal—not deficient—because vitamin D deficiency causes a lot of problems.”
Officially, deficiency is defined as having less than 20 nanograms per milliliter (ng/mL) of calcidiol, the circulating form of vitamin D, in the blood. But there’s a lot of debate about where the bar should be set, with many calling for levels of 30 or 40 ng/mL as the lower limit. But there’s no need for healthy people to run out and get tested. Just be sure you get your 600 units of vitamin D per day—and don’t be afraid to get a little extra.
When the Institutes of Medicine set vitamin D’s RDA in 2010, it upped the vitamin’s “tolerable upper limit” for adults—the level deemed safe for most people in that group—from 2,000 to 4,000 units per day. “So up to 4,000, you’re okay. If you go above that, you’re taking a risk,” says DeLuca, who currently takes around 3,000 units per day between food and supplements.
Pike, like DeLuca, isn’t waiting for the results of the VITAL study or new government guidelines to up his dose. After reading enough promising research studies, Pike made a decision: “I said I’ll take 4,000 units, just in case.”