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Code breakers: CEO Hugh Martin (left) and CTO Stephen Turner with their prototype.

Pacific Biosciences says it will soon be able to decipher the genetic code faster and cheaper than ever.

Michael V. Copeland, Fortune Magazine — It took the Human Genome Project $3 billion and 13 years to map the first genome and reduce it to a chemical code six billion letters long. Today, with faster computers and improved techniques, a research laboratory can sequence your DNA in about six weeks at a cost of $100,000 to $300,000.

Now a startup called Pacific Biosciences vows to do the job in 15 minutes for less than $1,000. The Menlo Park, Calif., outfit says that by 2013 it will have a microwave-oven-sized machine on the market that could bring genomics to the masses.

The device’s potential is sparking electric anticipation among some in the genetics community. “In all the things that I have seen in the past 20 years, I haven’t seen anything as disruptive as what PacBio is cooking up,” says Dr. Eric Topol, head of Scripps Genomic Medicine Program in La Jolla, Calif. “It changes everything in genomics.”

If a gene sequence could be ordered up as easily as an MRI – and the genetic blueprints of hundreds of thousands of individuals compiled – scientists could zero in on the mutations that cause Alzheimer’s, leukemia, or prostate cancer; pharmaceutical companies could design more precise drugs; and doctors could predict what infirmities you are likely to face and start to head them off.

The prototype, slightly bigger than a kitchen stove, bristles with tubes, lasers, lenses, and mirrors. It is a virtuoso feat of engineering that draws on optical networking, materials science, biophysics, and even a little videogaming.

A tiny zipper

First, a solution made up of DNA that has been cut into tiny strips is introduced into the machine. Then those strips are scattered over a thin metal sheet punctuated with 3,000 tiny holes about 70 nanometers (1/1,000th the thickness of a human hair) in diameter. Anchored to each hole is a special enzyme called DNA polymerase, whose job in nature is to travel down a strand of DNA like a zipper, splitting the double helix and creating a complementary image of each strand.

What the PacBio device does, in the words of company founder and chief technology officer Stephen Turner, is “eavesdrop on nature” by washing the array of DNA polymerase molecules with a specially modified solution of nucleotides. Each has been labeled with a phosphorescent dye that can be detected in a tiny illuminated zone at the bottom of the metal sheet. Whenever a nucleotide is incorporated into the growing chain of DNA, its fluorescent label flashes a distinctive color. By detecting and recording these flashes, the PacBio device builds a record of the precise sequence of base pairs in each strip of DNA. That record is fed into a computer that compiles the results from all the strips and reassembles them in the proper order.

PacBio’s prototype can sequence a gene at the rate of ten base pairs per second. But the finished machine will be even faster. It will operate like a massively parallel computer, churning out genetic code at speeds approaching 10,000 base pairs a second.

PacBio is not the only company pursuing this market, which analysts say could jump from its current $1.5 billion in revenues to tens of billions. Illumina (ILMN), Applied Biosystems (ABI), and Helicos BioSciences (HLCS) have already gone public; Complete Genomics and VisiGen Biotechnologies are still private. But CEO Hugh Martin is confident that PacBio, which is backed by blue-chip venture capital firms including Mohr Davidow and Kleiner Perkins, will be the first to get a fast and cheap product on the market.

Indeed, such is the excitement about PacBio’s device that one health-care technology analyst even brings up the G-word. Says Ross Muken of Deutsche Bank: “These guys have a shot at becoming the Google of health care, the company that comes out of nowhere and dominates.”

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Gene map: A genetic map of Europe (above) compared with its geographic equivalent (below). The genetic map shows each of the 1,387 individuals represented by a color and a country, according to the country of origin of all four of their grandparents. The plotted points are relative to each other in terms of the similarity or dissimilarity of 200,000 single nucleotide polymorphisms–variations at single points along the genome. The larger country labels represent the center points of these populations, according to the distribution of their genetic populations. The positions of these center points appear to closely map the geographical positions of the countries involved.
Credit: John Novembre

Researchers create a picture of Europe by mapping genetic variation among Europeans.

By Duncan Graham-Rowe, September 3, 2008, MIT Technology Review – Scientists have shown that they can use genomic analysis to pinpoint a person’s geographical origins to within just a few hundred kilometers. Besides offering possibilities for the testing of genetic ancestry, the research could also have important implications for understanding the role of genes in complex diseases and other genomic-based health studies.

By plotting the differences between genetic variations of 3,000 Europeans in a two-dimensional grid, the researchers were able to reveal a pattern that looks remarkably like Europe. The scientists included researchers from Cornell University; the University of California, Los Angeles (UCLA); the University of Chicago; and the University of Lausanne, in Switzerland. The findings appear in this week’s issue of Nature.

Others have recently published similar research, in Current Biology, says John Novembre, a coauthor of the Nature paper and an assistant professor at UCLA. But the latest study goes further, by using algorithms to try to predict a person’s geographical origin based purely on his or her genetic variations, with a high degree of accuracy. The scientists were even able to reveal patterns of origin distinguishing French-, German-, and Italian-speaking groups within Switzerland.

In many respects, the results are not at all surprising, says Michael Krawczak of the Institute for Medical Informatics and Statistics at the Christian-Albrechts University of Kiel, in Germany, who took part in the Current Biology study. It was well established that the farther apart two people’s origins, the more different their genes will be, he says. “But it had never been shown before at a genome-wide level.”

One of the reasons that this is now possible is the plummeting cost of genotyping, says Novembre. The Affymetrix GeneChip measures 500,000 single nucleotide polymorphisms (SNPs)–variations at a single point in the genome–for just a few hundred dollars, he says.

Genetic samples were chosen to include individuals whose geographic ancestry could be determined, based on having all four grandparents coming from the same country.

The researchers then created a two-dimensional map with individuals positioned according to how similar or how different they are from all the others. When color-coded to show where each of their grandparents is from, the results are compelling, clearly showing the shape and boundaries of Europe.

One of the motivations for this kind of work is to assist genetic epidemiology, or population-wide genetic studies. Indeed, this is one of the main goals of Glaxo Smith-Kline, which participates in the study, says Novembre. “They are interested in pharmacogenetic purposes to do case control studies of adverse drug reactions,” he says.

“The idea is to save money in these large-scale genetic epidemiological studies,” says Krawczak. “It’s very costly to genotype people.” But if you can create genetic control groups for distinct populations, it allows you to more easily test drugs against different populations to see where the benefits lie, he says.

At the moment, the main focus is on Europe because it has a lot of genetic variation but a relatively well defined and delineated history. “It’s a nightmare to do population genetics in America,” says Krawczak. “There are so many migrant populations from different parts of the world that it’s just too complex.”

Even so, Novembre says that he plans to extend this sort of research to cover larger parts of the world and individuals of mixed ancestry. “At the moment, if you have mixed grandparent ancestry you appear between the set of countries where the grandparents come from,” he says. “So if they are part Italian and part British, they would appear in Switzerland. But we are working on algorithms that will be able to infer grandparent ancestry and get around this.”

Eventually, this sort of research is likely to be picked up by the growing number of companies offering DNA home tests over the Internet to people wishing to trace their genealogy. At the moment, these services tend to offer fairly rough pictures of one’s origins. But as the microarray technology becomes cheaper and the statistical software used to map it becomes more sophisticated, these kinds of services should greatly improve, Novembre says.

The deal boom isn’t over for drugmakers.

By Telis Demos, NEW YORK Fortune.com — Overall, dealmaking may be in a slump, but Big Pharma has been buying up biotech firms at a record pace – it’s now the fastest-growing M&A sector, with deal value up 87% this year.

Of the 32 deals proposed in 2008, the biggest is Roche’s $44 billion bid for total control of Genentech (DNA), the biotech shop of which it already owns a controlling share. Another headline grabber is Bristol-Myers’ (BMY, Fortune 500) $4.3 billion offer for ImClone (IMCL) (yes, of the Martha Stewart scandal).

The deals are a big departure from the past, when cheaply licensing a single drug was the standard. “This was unthinkable a few years ago,” says Steven Wilcox, head of life sciences M&A at Ropes & Gray. “In licensing, you pay a little bit up front and a lot on the back end, but only if the drug is successful. In a merger, it’s all the cost up front.” That makes them more expensive and much riskier deals.

Pharmaceutical companies are spending their mountains of cash piled up from years of strong sales. Globally, the industry sold $712 billion worth of drugs in 2007. Yet the industry is expected to lose billions of dollars of revenue as top-selling drugs lose patent protection, and generic makers sweep in to sell much cheaper versions of the same drugs. The best-selling drug in the world, Pfizer’s (PFE, Fortune 500) Lipitor, generated $8.1 billion in sales in 2007 – its patent will expire in 2011.

Big Pharma’s sales are expected to grow about 4.5% in 2008, according to S&P analyst Steven Silver, down from 6% growth last year. Shares of pharmaceutical companies trade an at average multiple of 13 times earnings, or about a 15% discount to the overall market.

That’s where biotech drugs come in. First, the biotech sector promises to deliver the next generation of blockbusters. Genentech’s Avastin and ImClone’s Erbitux could both potentially treat dozens of different kinds of cancers, if the FDA approves their use as broadly as the companies want.

Second, biotech drugs still aren’t subject to the same patent rules as traditional chemical-based drugs so generic drugmakers aren’t yet a major threat. This means that biotech drugs could give drug companies predictable long-term revenues rather than relatively short-terms bursts of cash. Congress is still debating the rules on how to patent what is essentially a biological organism. According to research firm Global Insight, the FDA won’t consider approving biological generics until Congress has provided guidelines.

The technology to create generic biotech drugs also isn’t widely available, which makes drug development very expensive. High costs and the prospect of new U.S. and European rules governing production and patents are driving consolidation among generic makers too. In January, Israeli generic giant Teva Pharmaceuticals (TEVA) bought Maryland-based rival CoGenesys for $400 million. Teva is rumored to be interested Germany’s Stada for the same reason.

Overall, biotech sales are expected to rise 13% this year, according to health-care research firm IMS Health. Shares of biotech companies advanced 10% in the first half of 2008, compared to a 13% fall for healthcare generally.

It’s no surprise, then, that Big Pharma is willing to pay hefty premiums (often 30% or more) and take on a lot of risk to get into the market. It will ensure exclusive access for them to future drug discoveries – and replenish their own dry pipelines.

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Mario Tama/Getty Images
SLEEVES UP The elderly, who account for most influenza deaths, have been urged for decades to receive annual vaccinations.

Losing its reputation as an effective way to ward off the virus in the elderly?

By Brenda Goodman, September 3, 2008, The New York Times – The influenza vaccine, which has been strongly recommended for people over 65 for more than four decades, is losing its reputation as an effective way to ward off the virus in the elderly.

A growing number of immunologists and epidemiologists say the vaccine probably does not work very well for people over 70, the group that accounts for three-fourths of all flu deaths.

The latest blow was a study in The Lancet last month that called into question much of the statistical evidence for the vaccine’s effectiveness.

The authors said previous studies had measured the wrong thing: not any actual protection against the flu virus but a fundamental difference between the kinds of people who get vaccines and those who do not.

This contention is far from universally accepted. And even skeptics say that until more effective measures are found, older people should continue to be vaccinated, because some protection against the flu is better than none.

Still, the Lancet article has reignited a longstanding debate over claims that the vaccine prevents thousands of hospitalizations and deaths in older people. “The whole notion of who needs the vaccine and why is changing before our eyes,” said Peter Doshi, a doctoral candidate at M.I.T. who published a paper on the historical impact of influenza in May in The American Journal of Public Health.

The Lancet paper, by Michael L. Jackson and colleagues at the Group Health Center for Health Studies in Seattle, was based on an analysis of medical charts of thousands of elderly members of an H.M.O.

The study found that people who were healthy and conscientious about staying well were the most likely to get an annual flu shot. Those who are frail may have trouble bathing or dressing on their own and are less likely to get to their doctor’s office or a clinic to receive the vaccine. They are also more likely to be closer to death.

Dr. David K. Shay of the Centers for Disease Control and Prevention, a co-author of a commentary that accompanied Dr. Jackson’s study, agreed that these measures of health and frailty “were not incorporated into early estimations of the vaccine’s effectiveness” and could well have skewed the findings.

Not everyone is sold on the significance of the Lancet study. “I think this is another study that provides interesting findings and raises questions,” said Dr. Kristin Nichol, chief of medicine at the Veterans Affairs hospital in Minneapolis. “I don’t think we know yet what the final word is on influenza vaccinations in the elderly.

“I really feel, and I feel very strongly about this, that the public health message should be that vaccines are effective,” she continued. “I don’t think that science is necessarily best hashed out in the media.”

Dozens of studies since 1960 have supported the view that the vaccine is a powerful protector of the elderly, cutting their risk of dying in winter from any cause by almost 50 percent and reducing the risk of hospitalization by nearly 30 percent.

Those findings came from observational studies, in which scientists make inferences about the effect of a treatment on a population by comparing what happens to a group that has the treatment with what happens to an apparently similar group that does not.

There has been only one large study that compared the flu vaccine with a placebo for two random groups of older people in which neither the patients nor the scientists knew which group was receiving which injection. It came to a different conclusion from the observational studies.

Conducted by Dutch researchers and published in 1994 in The Journal of the American Medical Association, it found that in those 60 to 69, the vaccine prevented influenza about 57 percent of the time. In those over 70, the vaccine prevented the flu just 23 percent of the time, though the estimate is imprecise because the study was not designed to look at this age group.

But the influenza vaccine was never put through more placebo-controlled trials, which are considered the gold standard in medical evidence. “I think the evidence base we have leaned on is not valid,” said Lone Simonsen, an epidemiologist and visiting professor at the George Washington University School of Public Health and Health Services in Washington who was not connected with the Lancet study.

In 2005, Dr. Simonsen, who was then at the National Institute of Allergy and Infectious Diseases in Bethesda, Md., published a paper in The Archives of Internal Medicine that found something odd: even though the percentage of older people who got an annual flu shot more than tripled from 1980 to 2001, there was no corresponding drop in the death rate.

That paper included one of the first estimates of how many deaths are actually caused by the flu — a number hard to pin down because doctors seldom confirm flu in their patients with lab tests. Using a statistical model and the best available data, Dr. Simonsen found that influenza probably causes just 5 to 10 percent of all winter deaths in the elderly. But earlier studies had found that the flu vaccine cut an elderly person’s risk of dying by 50 percent.

“You don’t have to do a whole lot of math to realize that doesn’t add up,” said Dr. Lisa A. Jackson of the Group Health Center for Health Studies in Seattle, who has also studied the effectiveness of the flu vaccine in the elderly.

Dr. Jackson at first tried to tease out underlying differences between vaccinated and unvaccinated elderly people by using medical codes — a numerical shorthand that doctors use to classify and record what is wrong with their patients. She and other researchers reasoned that patients with codes for cancer or heart disease, for example, might be very sick, thus skewing the results. When they adjusted for those codes, however, the differences between the vaccinated and unvaccinated groups became even more pronounced. The vaccine looked even more protective.

It was Michael L. Jackson’s thesis project, at the University of Washington, that revealed the flaw in using the codes to differentiate patients.

For the project, Mr. Jackson (no relation to Lisa Jackson) and three other researchers spent almost three years reading medical charts and examining X-rays. They discovered that health-conscious people were more likely to get medical codes for things like heart disease and cancer simply because they went to the doctor more often. But when Mr. Jackson adjusted for measures of frailty — things like lung function, whether people needed help bathing or dressing, and what kinds of medications they took — he found that vaccination had little effect on older people’s risk for pneumonia, the most dangerous complication of the flu.

That finding has a biological basis. Vaccines work by priming the immune system to recognize and respond to incoming threats. Because the immune system slows down with age, older adults do not respond as well to vaccines as younger adults.

A recent study by Dr. Wilbur H. Chen and colleagues at the Center for Vaccine Development at the University of Maryland School of Medicine found that elderly participants needed four times the amount of antigens given in a standard dose of the flu vaccine to have the same kind of immune response as healthy adults under 40. They presented their findings in May at the Annual Conference on Vaccine Research in Baltimore.

Despite these findings, Dr. Shay said the C.D.C. had no plans to change its vaccine recommendations, though he added that the agency had financed studies to look for more effective influenza vaccines for the elderly.

Dr. Simonsen, the epidemiologist at George Washington, said the new research made common-sense infection-control measures — like avoiding other sick people and frequent hand washing — more important than ever. Still, she added, “The vaccine is still important. Thirty percent protection is better than zero percent.”

All sixth-graders must get shots in New Jersey

By Alison Herget, September 2, 2008, APP.com – It’s a disease that can start out with a headache, stiff neck, perhaps a high fever.

But when it takes its toll, it can be fatal in less than a day. And it is more deadly to adolescents than adults.

Bacterial meningitis, an infection of the fluid of a person’s spinal cord and the fluid that surrounds the brain, is a rare but serious condition, according to health experts.

But when thousands of New Jersey sixth-graders head back to school this year, their chances of being stricken with the disease will be significantly reduced.

That’s because for the first time, the state is requiring all children in that age group to get a meningococcal vaccine that protects against most types of the bacterial form of the disease.

“It’s the kind of disease where you wake up in the morning and you have a little bit of a scratchy throat, and before the sun goes down you’re dead,” said Dr. Meg Fisher, medical director of The Children’s Hospital at Monmouth Medical Center. “So it can be a very rapidly progressing infection that occurs in otherwise healthy children and young adults.”

Four new immunizations for children, including one that prevents most types of bacterial meningitis, were approved in December by state Health and Senior Services Commissioner Dr. Fred Jacobs. The new requirements also call for preschoolers to receive flu and pneumococcal vaccines and sixth-graders to get a whooping cough booster shot.

Along with that call comes stepped-up efforts from least one advocacy group that says children are getting too many shots too soon, and has pressured the Legislature to give parents more choice with immunizations.

But health experts who support the increased immunizations counter the numbers speak for themselves.

Each year, nearly 3,000 cases of meningococcal disease are reported in the United States, and 10 to 12 percent — or 300 to 360 of them — are fatal, according to the Centers for Disease Control and Prevention. There are two types of meningitis: Bacterial meningitis is the more severe of the two, and can result in result in brain damage, hearing loss, learning disability or even death, according to the CDC Web site. Viral meningitis is serious but rarely fatal in people with normal immune systems. It cannot be prevented with the vaccine but usually resolves without specific treatment.

That fatality rate for meningococcal disease can be as high as 20 percent in adolescents, said Dr. Aswine Bal, director of pediatric infectious disease at K. Hovnanian Children’s Hospital at Jersey Shore Medical Center, Neptune. And that’s one reason why it’s so important to vaccinate, he said.

“Meningococcal disease is not very common,” he said. “But the disease can start fast. And sometimes (the patients) are dying before the even come to the hospital.”

Dr. Tina Tan, acting state deputy health commissioner/epidemiologist, said the state’s move to require the meningococcal vaccine for 11- and 12-year-olds mirrors recommendations from the CDC.

Many states, including New Jersey, have required for years that college students get vaccinated because of their lifestyle. The disease, which can be transmitted by direct contact or through air droplets, is more easily transmitted among students living in dormitories or close quarters.

“This is smart medicine,” Fisher said of the state’s move to require the vaccine. “This is not overkill. It’s a very bad bacterial infection, and it’s good to protect your children.”

However, some believe that it is not the state’s place to be piling on more mandated vaccines for children each year. Although scientific research has not shown a relationship between vaccines and autism, critics say requiring more and more vaccines is a risk that should not be taken.

“As with all medical procedures there are risks involved, and parents should have the right to choose whether or not they want to take these risks,” said Cathy Millet, co-founder for the New Jersey Alliance for Informed Choice in Vaccination, an advocacy group.

September 3, 2008, Harvard Medical School Review – Using sunscreen and avoiding the midday sun are mainstays of skin cancer prevention. However, many vitamin D researchers believe that by diligently shielding ourselves from sunlight we might be missing out on the many benefits of this powerhouse vitamin, which is made when our skin is exposed to ultraviolet light.

Ultraviolet B (UVB) rays cause sunburn and the cell damage that leads to skin cancer, although research implicates ultraviolet A (UVA) rays as well. But it’s the energy from UVB that penetrates the skin and eventually becomes the biologically active form of vitamin D.

Active vitamin D helps regulate how cells grow and mature, so in some circumstances it may put the brakes on cancerous runaway cell growth. Vitamin D also helps keep the immune system in line, which may be the reason animal and epidemiological studies hint at a connection between low vitamin D levels and autoimmune disorders such as type 1 diabetes and multiple sclerosis.

Fortunately, a sizable patch of middle ground exists between the two camps that acknowledges the dangers of sun exposure while giving vitamin D its due.

The winter filter

During the winter in the upper latitudes (roughly 40° — the latitude of New York City — or higher) of the Northern and Southern hemispheres, sunlight hits the earth at an angle, so it travels a longer distance through the atmosphere. Much, if not all, of the UVB gets filtered out (although the longer waves of UVA still get through). Sunburn isn’t a problem, but blood levels of vitamin D drop to about half of their summertime levels.

Apart from the risk of UVB, added sun exposure won’t fix many people’s vitamin D woes. With age, the skin’s capacity for making vitamin D diminishes, so the effect of getting more sun is going to be limited in older folks. And the melanin that makes skin dark effectively filters out UVB, so African Americans are much more likely than whites to have low levels of vitamin D. Researchers in sun-drenched Arizona reported in 2008 that over half of the African Americans in their colorectal cancer study had low vitamin D levels, defined as 20 nanograms per milliliter (ng/ml).

Diet and supplements

Government guidelines say people between the ages of 51 and 70 should get 400 International Units (IU) of vitamin D daily, and those ages 71 and older, 600 IU. Many experts say Americans should shoot for 1,000 IU, because, on average, that’s how much it takes (along with incidental sun exposure) to get the levels in the blood to 30 ng/ml, the level at which prevention of cancer and other diseases seems to kick in.

Unfortunately, there are only a few good food sources of vitamin D: salmon (about 350 IU per 3½-ounce serving), mackerel, sardines, and other kinds of oily seafood are about it. In the U.S., milk and some brands of orange juice are artificially fortified with 100 IU per 8 ounces. Some breakfast cereals are also fortified.

Traditionally, supplement makers have used vitamin D2 (ergocalciferol), particularly in multivitamin pills. Some data show little difference in the effects of D2 and D3 (cholecalciferol), the form used to fortify milk and contained naturally in fish, but the conventional wisdom has been that D2 is about a third to a fourth less effective than D3 at increasing blood levels of vitamin D. Because D3 has been presumed to be more potent, it is increasingly the form used in vitamin D and vitamin D-calcium supplements.

You can get too much vitamin D, but the level where toxicity is seen is almost certainly many times higher than the upper daily limit of 2,000 IU set by the Institute of Medicine. For years, vitamin D researchers have wanted a re-evaluation of vitamin D minimums and maximums, but so far, this hasn’t happened.

Here’s an Excerpt from the Vitamins and Minerals Special Health Report

What’s special about vitamin D? This fat-soluble vitamin is exceptional among vitamins in three ways. First, it has a unique mechanism of action in the body. Second, you can’t get very much of it naturally through your diet. And third, many Americans are deficient in this vital nutrient. That final point is keenly important, in light of burgeoning evidence that vitamin D’s health benefits extend far beyond its reputation for building healthy bones. Over the past decade, studies suggest that adequate amounts of vitamin D may lessen the risk of several types of cancer (including cancers of the colon, prostate, and breast) and may also play a role in preventing high blood pressure, multiple sclerosis, and even schizophrenia. And a 2007 meta-analysis of 18 randomized controlled trials showed that vitamin D supplementation may even help people to live longer.

How D is different

Unlike other vitamins, which are antioxidants or key players in enzyme reactions in the body, vitamin D functions in the body as a hormone—that is, a substance made by one organ that sends a chemical message to another organ to elicit a specific response. One of vitamin D’s best-known and important roles is to signal the intestines to absorb calcium into the bloodstream. Without sufficient vitamin D, your body will break down bone to get the calcium it needs—no matter how much calcium you consume through food and supplements. Vitamin D is also unusual be- cause it’s relatively scarce in normal diets. To get just 400 international units (IU) of vitamin D (the current recommended daily amount for people ages 50–71), you’d need to eat about 5 ounces of salmon, 7 ounces of halibut, 30 ounces of cod, or a 6-ounce can of tuna, or drink four cups of milk. Few people include that much fish—or milk, for that matter— in their daily fare. Milk actually doesn’t normally contain vitamin D, but nearly all the milk sold in the United States today is vitamin- D fortified. This practice began in the 1930s to combat rickets, a disease that leads to soft, weak bones caused by vitamin D deficiency. It’s worth noting that dairy products made from milk, such as cheese, yogurt, and ice cream, aren’t typically fortified with vitamin D and contain only small amounts.

In fact, casual exposure to sunlight provides people with most of their vitamin D requirement (see Figure 5). Sunlight contains two forms of radiant energy, ultraviolet A (UVA) and ultraviolet B (UVB). UVB provides the energy your body needs to generate vitamin D, which is why it’s known as the “sunshine vitamin.” If you sit outside on a sunny day in the middle of summer at the equator wearing only a swimsuit, your body creates a whopping 20,000 IU of vitamin D per hour. But even people who don’t sunbathe or spend a great deal of time outside probably generate a fair amount just walking outside for short periods throughout the day, depending on the latitude and the amount of skin that is exposed. However, a number of factors—including the season, time of day, and where you live—can affect how much UVB reaches your skin. What’s more, your age, skin color, and sunscreen use also influence your skin’s production of vitamin D. A confluence of these factors can conspire to limit vitamin D levels, which is why a surprisingly large number of Americans—more than 50% among certain groups—are deficient in vitamin D.