Chapter 5. Hormones and the Brain
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Steve Connor Having children can permanently affect the brain of women because the surge in female sex hormones during pregnancy can influence the development of key parts of the central nervous system, a series of studies has shown. The findings suggest that childbirth can affect the female brain, but they could also shed light on the controversy over whether hormone replacement therapy in menopausal women affects the risk of developing Alzheimer’s disease in later life, scientists said. The research looked at two of the oestrogen hormones used to treat the symptoms of menopausal women and found that they could have a complex effect depending on the age of the women and whether or not they had previously given birth. Although the work was mostly carried out on laboratory rats, the scientists said that the findings are more widely applicable to humans because the same hormones and brain cells are involved. The scientists found that the surge in oestrogen hormones during pregnancy, where levels can soar to several hundred times normal levels, can alter “neuroplasticity” or the re-growth of nerve cells in a part of the brain called the hippocampus, which is responsible for aspects of memory and spatial awareness. “Our most recent research show that previous motherhood alters cognition and neuroplasticity in response to hormone therapy, demonstrating that motherhood permanently alters the brain,” said Liisa Galea of the University of British Columbia in Vancouver, Canada.
By John Horgan The New York Times "Sunday Review" section has anointed Richard Friedman its go-to guy for touting behavioral genetics--or "gene-whiz science," as I prefer to call it. In March, Friedman, professor of clinical psychiatry at Weill Cornell Medical College, proclaimed that researchers had discovered a "feel-good gene," which "makes some people inherently less anxious, and more able to forget fearful and unpleasant experiences." As I pointed out on this blog, Friedman's claim—like virtually all reported linkages of complex human traits and disorders to specific genes (see Further Reading)--is based on flimsy, contradictory evidence. I'm so naïve, or arrogant, that I actually thought my critique might dissuade the Times from further hype of gene-whiz science. Times editors must care more about traffic than accuracy, because they devoted almost the entire front page of yesterday’s "Sunday Review" to Friedman's latest travesty, "Infidelity Lurks in Your Genes." The core of Friedman's essay is his assertion that some women are "biologically inclined to wander." More specifically, women who carry variants of the gene AVPR1A—which encodes the receptor for the hormone arginine vasopressin--are "much more likely to engage in 'extra-pair bonding,' the scientific euphemism for sexual infidelity." In support of this claim, Friedman cites a study of Finnish twins and non-twin siblings by a team led by Australian psychologist Brendan Zietsch. The team surveyed the Finnish subjects and found that 9.8 percent of the men and 6.4 percent of the women reported engaging in at least one "extra-pair mating." The researchers found an association between five AVPR1A markers and extra-pair mating in women but not in men.
Richard A. Friedman AMERICANS disapprove of marital infidelity. Ninety-one percent of them find it morally wrong, more than the number that reject polygamy, human cloning or suicide, according to a 2013 Gallup poll. Yet the number of Americans who actually cheat on their partners is rather substantial: Over the past two decades, the rate of infidelity among married men has been pretty constant at around 21 percent, while the percentage of married women who admitted to cheating has mostly hovered between 10 and 15 percent, according to the General Social Survey at the University of Chicago’s independent research organization, NORC. We are accustomed to thinking of sexual infidelity as a symptom of an unhappy relationship, a moral flaw or a sign of deteriorating social values. When I was trained as a psychiatrist we were told to look for various emotional and developmental factors — like a history of unstable relationships or a philandering parent — to explain infidelity. But during my career, many of the questions we asked patients were found to be insufficient because for so much behavior, it turns out that genes, gene expression and hormones matter a lot. Now that even appears to be the case for infidelity. We have long known that men have a genetic, evolutionary impulse to cheat, because that increases the odds of having more of their offspring in the world. But now there is intriguing new research showing that some women, too, are biologically inclined to wander, although not for clear evolutionary benefits. Women who carry certain variants of the vasopressin receptor gene are much more likely to engage in “extra pair bonding,” the scientific euphemism for sexual infidelity. © 2015 The New York Times Company
|By Julie Hecht Unlike porcupines, dogs are a relatively hands-on (actually, paws-on) species, both with one another and with us. YouTube has numerous videos of dogs essentially saying, “Just keep petting me, please. Yes, that’s it…more.” But this relationship is not one-sided. Many studies find that positive interactions between people and dogs can be beneficial for both species. Increases in β-endorphin (beta-endorphin), oxytocin and dopamine—neurochemicals associated with positive feelings and bonding—have been observed in both dogs and people after enjoyable interactions like petting, play and talking. Essentially, interacting with a dog, particularly a known dog, can have some of the same psychophysiological markers as when two emotionally attached people spend time together. But do certain types of interactions have an outsized impact? Dogs are incredibly attentive to human faces and, in some cases, even specific facial expressions. This seemingly routine, benign behavior—your dog turning to gaze on your beautiful face as you do his or hers—could actually hold a very important piece of the puzzle in our relationship with dogs, suggests a study published this week in Science. The new study, by Miho Nagasawa of Azabu University in Japan and colleagues, builds on Nagasawa’s previous work, published in Hormones and Behavior in 2009, that found owners and dogs sharing a long mutual gaze had higher levels of oxytocin in their urine than owners of dogs giving a shorter gaze. (Oxytocin, a humble peptide of nine amino acids that is sometimes called the “cuddle hormone,” has been implicated in social bonding and is instrumental to the cascade of hormonal changes leading up to and following birth.) Nagasawa and her colleagues concluded that their finding was “a manifestation of attachment behavior.” © 2015 Scientific American
By Virginia Morell Like many newborn mammals, baby mice cry to get their mother’s attention. But the mother doesn’t instinctively recognize these calls; she must learn the sounds of her offspring—just as human parents must learn the cries of their infants. Now, a team of researchers has discovered that the hormone oxytocin, which has been tied to trust and maternal bonding, holds the key to how this learning occurs. Only after oxytocin tweaks the brain of a female mouse does she respond with a mother’s concern and attentiveness to crying pups. “It’s an exciting study with implications that … could be helpful to certain disorders, such as autism,” says Larry Young, a neuroscientist at Emory University in Atlanta who was not involved in the work. To understand the role oxytocin plays in a mother mouse’s brain, scientists at New York University School of Medicine first investigated how female mice in general respond to the distress calls of baby mice. Pups emit ultrasonic cries when they are separated from the nest, which sometimes happens when a mother carries her babies to a new location. (Moms change nest locations regularly to elude predators.) When a mother hears these cries, she runs to the lost pup, picks it up, and carries it back to her nest. Other scientists have shown that moms respond even to the distress cries of pups that aren’t their own, readily approaching loudspeakers that broadcast the calls. Most virgin female mice, though, couldn’t care less; they seem completely indifferent to the pups’ cries for help. And yet, some virgin females that have either been housed with a mother and her litter or have been injected with oxytocin will retrieve crying infants. © 2015 American Association for the Advancement of Science.
By Nicholas Weiler Killer whales wouldn’t get far without their old ladies. A 9-year study of orcas summering off the southern tip of Vancouver Island in the Pacific Northwest finds that menopausal females usually lead their families to find salmon, particularly when the fish are scarce. Older females’ years of foraging experience may help their clans survive in years of famine, an evolutionary benefit that could explain why—like humans—female orcas live for decades past their reproductive prime. “Menopause is a really bizarre trait. Evolutionarily it doesn’t make sense,” says biologist Lauren Brent of the University of Exeter in the United Kingdom, who led the new study. Most animals keep having babies until they drop, part of the evolutionary drive to spread their genes as widely as possible. Only female humans, pilot whales, and killer whales are known to go through menopause: At a certain age, they stop reproducing, but continue to lead long, productive lives. Like humans, female killer whales stop giving birth by about 40, but can live into their 90s. Anthropologists have proposed a controversial explanation for menopause in humans: that grandmothers contribute to their genetic legacies by helping their children and grandchildren survive and reproduce. In hunter-gatherer and other societies, elders find extra food, babysit, and remember tribal lore about how to live through floods, famines, and other hardships. According to the “grandmother hypothesis,” this contribution is so valuable that it helped spur the evolution of women’s long postreproductive lives. Orcas too depend on their elders: Adult killer whales’ mortality rates skyrocket after their elderly mothers die. But how the menopausal whales might help their children survive was not clear, Brent says. © 2015 American Association for the Advancement of Science.
by Michael Slezak If you want to counteract the effects of getting drunk, a big dose of the so-called "cuddle-chemical" oxytocin might be the answer. Oxytocin has important roles in sexual behaviour and social bonding, and has previously been investigated as a way to help wean alcoholics off drink. While studying this effect in rats, Michael Bowen from the University of Sydney noticed something strange. Rats that had been given oxytocin didn't seem to get drunk. "Those that had the oxytocin were up and moving about as if they hadn't had any alcohol at all, whereas the ones that didn't have oxytocin were quite heavily sedated," Bowen says. This effect was confirmed in a second experiment, in which half the rats were given an injection of oxytocin straight into the brain, at a level about 150,000 times what would normally be found there. They were then given alcohol, after which researchers tested their motor control and reaction times. Oxytocin seemed to completely counteract the effects of the booze – even when a rat had consumed what would be equivalent to about one and a half bottles of wine in humans. "The rats that had received oxytocin, as well as the alcohol, were virtually indistinguishable from the rats that hadn't received any alcohol at all," says Bowen. This could be thanks to the brain's GABA receptors, where alcohol is thought to exert its intoxicating effects. Bowen's team found that oxytocin was binding to two parts of these receptors, blocking alcohol from getting there. "It was actually preventing alcohol affecting these sites in the brain that make you intoxicated." © Copyright Reed Business Information Ltd
By Anne Harding NEW YORK (Reuters Health) - Reduced sexual activity could cause a dip in testosterone levels in older men, new findings suggest. Among men 70 and older, those who reported a decline in sexual activity and desire over a two-year period also showed small declines in serum testosterone, Dr. David Handelsman of the ANZAC Research Institute at the University of Sydney and Concord Hospital in New South Wales, Australia, and colleagues found. They report their findings in the Journal of Clinical Endocrinology and Metabolism, online January 28. "Decline in serum testosterone is more likely to be the result rather than the cause of sexual dysfunction among older men who don't have reproductive disorders," Dr. Handelsman told Reuters Health by email. "The widely prevalent misinterpretation of this (as if the mild lowering of serum testosterone needs or might benefit from testosterone treatment) is one of the main drivers of the massive over-use of testosterone prescriptions in North America over the last decade." While declines in androgens and sexual function are both thought to be aging-related, Dr. Handelsman and his colleagues note in their report, the relationship between androgen levels and sexual function is not clear. To better understand the temporal and predictive relationship between androgen levels and sexual function, the researchers looked at 1,226 men participating in the Concord Health and Ageing in Men Project (CHAMP), measuring their levels of testosterone, dihydrotestosterone, estradiol, and estrone with liquid chromatography-tandem mass spectrometry. Men also reported on their sexual function using standardized questions, at baseline and two years later. © 2015 Scientific American
By David Shultz The most venomous animal on the planet isn’t a snake, a spider, or a scorpion; it’s a snail—a cone snail, to be precise. The Conus genus boasts a large variety of marine snails that have adopted an equally diverse assortment of venoms. Online today in the Proceedings of the National Academy of Sciences, researchers report an especially interesting addition to the animals’ arsenal: insulin. According to the paper, this marks the first time insulin has been discovered as a component of venom. Not all cone snails incorporate insulin into their venom cocktail, wonderfully known as nirvana cabal; the hormone was found only in a subset of the animals that hunt with a netting strategy that relies on snaring fish in their large, gaping mouthparts. Unlike the feeding tactics of some cone snails that hunt using speedy venom-tipped “harpoons,” the mouth-netting strategy is a rather slow process. For it to work, the fish either needs to be very unaware of its surroundings or chemically sedated. Scientists speculate that it’s the insulin that provides such sedation. Snails like Conus geographus (seen above) actually produce multiple variants of the hormone, some of which, like one called Con-Ins G1, are more similar to fish insulin than snail varieties. Con-Ins G1 isn’t an exact match of fish insulin though; it’s a stripped-down version that the team suspects may be missing bits that would let fish detect the overdose and respond. If they’re correct, the snail’s venom may yield insight into the nuances of how insulin is regulated that may extend to humans. © 2015 American Association for the Advancement of Science
By Neuroskeptic A new study offers two reasons to be cautious about some of the claims made for the role of the hormone oxytocin in human behavior. The paper’s out now in PLoS ONE from researchers James C. Christensen and colleagues, who are based at the US Air Force Research Laboratory in Ohio. That the military are interested in oxytocin at all is perhaps a testament to the huge amount of interest that this molecule has attracted in recent years. Oxytocin has been called the “hug hormone”, and is said to be involved in such nice things as love and trust. But according to Christensen et al., quite a lot of previous oxytocin research may be flawed. Their paper is in two parts. Christensen et al. first show that the only accurate way to measure oxytocin levels in blood is by performing plasma extraction before chemical analysis. Using unextracted plasma, they find, leads to seriously distorted measures. The differences between extracted and unextracted plasma estimates of oxytocin have been noted before, but Christensen et al. show directly that unextracted plasma interferes with oxytocin measurement. They found that oxytocin test kits were unable to detect a ‘spike’ of pure oxytocin added to some unextracted plasma samples, whereas the spike was reliably detected when added to an extracted sample. This was true using either the ELISA or RIA method for quantification of oxytocin. With ELISA, unextracted oxytocin measures were also very noisy and unrealistically high:
Keyword: Hormones & Behavior
Link ID: 20479 - Posted: 01.14.2015
By Bethany Brookshire WASHINGTON — Estrogen can protect the brain from harmful inflammation following traumatic injury, a new study in zebra finches suggests. Boosting levels of the sex hormone in the brain might help prevent the cell loss that occurs following damage from injuries such as stroke. Estrogen levels quadrupled around the damaged area in both male and female zebra finches after researchers gave them experimental brain injuries, Colin Saldanha and colleagues at American University in Washington, D.C., reported November 17 at the annual meeting of the Society for Neuroscience. When the scientists prevented finch brains from making estrogen, inflammatory proteins at damaged sites increased. The helpful estrogen didn’t come from gonads. It’s made within the brain by support cells called astrocytes close to the injury. Injury inflames the brain. Initially, this inflammation recruits helpful cells to the damaged area and aids in recovery. But the long-term presence of inflammatory proteins can cause harm, killing off brain cells and reducing functions such as movement and memory. The researchers hope that by understanding how estrogen reduces inflammatory proteins, therapies might boost this natural estrogen production to keep harmful inflammation at bay. © Society for Science & the Public 2000 - 2014.
By Melissa Hogenboom Science reporter, BBC News A small group of neurons that respond to the hormone oxytocin are key to controlling sexual behaviour in mice, a team has discovered. The researchers switched off these cells which meant they were no longer receptive to oxytocin. This "love hormone" is already known to be important for many intimate social situations. Without it, female mice were no more attracted to a mate than to a block of Lego, the team report in journal Cell. These neurons are situated in the prefrontal cortex, an area of the brain important for personality, learning and social behaviour. Both when the hormone was withheld and when the cells were silenced, the females lost interest in mating during oestrous, which is when female mice are sexually active. At other times in their cycle they responded to the males with normal social behaviour. The results were "pretty fascinating because it was a small population of cells that had such a specific effect", said co-author of the work Nathaniel Heintz of the Rockefeller University in New York. "This internal hormone gets regulated in many different contexts; in this particular context, it works through the prefrontal cortex to help modulate social and sexual behaviour in female mice. "It doesn't mean it's uniquely responsible because the hormone acts in several important places in the brain but it does show that this particular cell type is required for this aspect of female social behaviour," Dr Heintz told BBC News. To silence the neurons, the team used toxins that block the ability of the cells to transmit signals to other neurons - technology that has recently revolutionised the ability to study small populations of neurons. BBC © 2014
BY Bethany Brookshire We all need sleep, but attaining it can be delicate. Insomniacs can’t fall or stay asleep. Travelers suffer from jetlag. Anxiety keeps people up at night. Or maybe it’s just that jackhammer running across the street keeping your eyes open. Some people turn to earplugs, dark curtains or alcohol to soothe them to sleep. But others go to the supplement aisle and pick up melatonin. The hormone melatonin is secreted from our brains at night and helps regulate sleep. But this chemical is not restricted to humans, or even to mammals. The roots of melatonin’s role in our nightly slumbers go back much further in evolutionary history. A new paper focuses in on the role of melatonin in tiny marine creatures called zooplankton. It turns out that these animals use melatonin just as much as we do, suggesting that the origins of sleeplike behavior may lie under the sea. “For every system and feature that makes a human or other animal today, you can ask the question: Where did it start? How did it begin? What was its first role and function, and how did it become more complex?” says study coauthor Detlev Arendt, a zoologist at the University of Heidelberg in Germany. Arendt’s laboratory has been studying the answers to these questions in the marine ragworm Platynereis dumerilii. This unassuming, centipede-like, ocean-dwelling worm produces larvae that float through the open water as zooplankton. These small larvae propel themselves up and down in the water column with movements of their cilia, slender, hair-like appendages that protrude out from the organisms. © Society for Science & the Public 2000 - 2014.
By Jennifer Balmer Each summer, leatherback sea turtles (Dermochelys coriacea) migrate thousands of kilometers from their tropical breeding grounds to feed in cooler waters. Yet how the animals know when to begin their long journey back south at the end of the season has mostly remained a mystery. New findings, to be published in an upcoming issue of the Journal of Experimental Marine Biology and Ecology, suggest that leatherback sea turtles may be able to sense seasonal changes in sunlight by means of an unpigmented spot on the crown of their head—known as the pink spot (pictured). Researchers conducted an examination of the anatomical structures beneath the pink spot and found that the layers of bone and cartilage were remarkably thinner than in other areas of the skull. This thin region of the skull allows the passage of light through to an area of the brain, called the pineal gland, that acts as biological clock, regulating night-day cycles and seasonal patterns of behavior. The authors suggest that the lack of pigment in the crowning pink spot and thin skull region underlying it act as a “skylight,” allowing the turtles to sense the subtle changes in sunlight that accompany changing seasons, signaling them to return south when autumn approaches. © 2014 American Association for the Advancement of Science
|By Gary Stix A biochemical produced in the brain called oxytocin has entered popular culture in recent years as the “love,” “cuddle” or “bonding” hormone. That’s a lot to choose from. Oxytocin plays a role in producing contractions at childbirth and in helping in lactation, but we’ve known that for more than a century. Experiments in the 1990s showed that it was instrumental in leading prairie voles, known for their monogamous behavior, to pick a lifelong mate. Later studies then demonstrated that the chemical contributes to trust and social interactions in various animals, including humans. After the vole study, interest in the nine–amino acid peptide started to rise. In a TED talk economist Paul Zak called it “the moral molecule” because of its link to trust, empathy and prosperity. The Internet DIY brain-makeover market then took up the meme. Vero Labs of Daytona Beach, Fla., sells “Connekt” oxytocin spray for $79 that purports to “strengthen workplace bonds” and “increase positive self-awareness.” The company has also come out with a his-and-her“Attrakt” spray that mixes oxytocin with pheromones—chemical sex attractants that help mice get it on, but whose role in triggering mating behavior in humans is hotly disputed. (Researchers who study oxytocin warn prospective buyers away from these purchases, saying that long-term use in humans has not been studied.) © 2014 Scientific American
By LISA SANDERS, M.D. On Thursday, we challenged Well readers to take on the case of a 19-year-old man who suddenly collapsed at work after months of weakness and fatigue dotted with episodes of nausea and vomiting. More than 500 of you wrote in with suggested diagnoses. And more than 60 of you nailed it. The cause of this man’s collapse, weakness, nausea and vomiting was… Addisonian crisis because of Addison’s disease Addison’s disease, named after Dr. Thomas Addison, the 19th-century physician who first described the disorder, occurs when the adrenal glands stop producing the fight-or-flight hormones, particularly cortisol and adrenaline and a less well known but equally important hormone called aldosterone that helps the body manage salt. In Addison’s, the immune system mistakenly attacks the adrenal glands as if they were foreign invaders. Why this happens is not well understood, but without these glands and the essential hormones they make, the body cannot respond to biological stress. The symptoms of Addison’s are vague. That’s one reason it’s so hard to diagnosis. Patients complain of weakness and fatigue. They often crave salt. And when confronted with any stress — an infection or an injury — patients with Addison’s may go into adrenal crisis, characterized by nausea and vomiting, low blood pressure and, sometimes, physical collapse. Their blood pressure may drop so low that oxygen-carrying blood cannot reach the extremities, causing skin to turn blue; if blood fails to reach even more essential organs, it can lead to death. © 2014 The New York Times Company
Keyword: Hormones & Behavior
Link ID: 20037 - Posted: 09.06.2014
By MATTHEW PERRONE AP Health Writer WASHINGTON (AP) — The Food and Drug Administration says there is little evidence that testosterone-boosting drugs taken by millions of American men are beneficial, though the agency is also unconvinced by studies suggesting the hormone carries serious risks. The agency posted its review online Wednesday ahead of a public meeting to discuss the benefits and risks of treatments that raise levels of the male hormone. Regulators agreed to convene the September 17 meeting after two federally funded studies found links between testosterone therapy and heart problems in men. The scrutiny comes amid an industry marketing blitz for new pills, patches and formulations that has transformed testosterone a multibillion-dollar market. Advertisements for prescription gels like Fortesta and Androgel promise aging men relief from ‘‘Low-T,’’ a condition they link to low libido, fatigue and weight gain. But FDA reviewers state that ‘‘the need to replace testosterone in these older men remains debatable.’’ While testosterone levels naturally decline after age 40, it’s unclear whether those lower levels actually lead to the signs commonly associated with aging, including decreased energy and loss of muscle. The FDA first approved testosterone injections in the 1950s for men who had been diagnosed with hypogonadism, a form of abnormally low testosterone caused by injury or medical illness. But the recent advertising push is focused on otherwise healthy men who simply have lower-than-normal levels of testosterone.
by Bethany Brookshire Premenstrual syndrome, or PMS, can be a miserable experience. Women report over 200 symptoms in the days before menstruation occurs. The complaints run the gamut from irritable mood to bloating. PMS can be so slight you don’t even notice, or it can be so severe it has its own category — premenstrual dysphoric disorder. But to some, PMS is just a punchline, a joke featured in pop culture from Buffy the Vampire Slayer to Saturday Night Live. Michael Gillings, who studies molecular evolution at Macquarie University in Sydney, thinks that PMS could have a purpose. In a perspective piece published August 11 in Evolutionary Adaptations, Gillings proposes that PMS confers an evolutionary advantage, increasing the likelihood that a woman will leave an infertile mate. He hopes that his idea could lead to more research and less stigma about the condition. But while his hypothesis certainly sparked a lot of discussion, whether it is likely, or even necessary, is in doubt. Gillings first began to think about PMS when he found out that premenstrual dysphoric disorder was being added to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders. “I started to think that we have a normal distribution of PMS responses, where some people don’t get any symptoms, the majority gets mild symptoms, and some get severe symptoms,” he explains. Including PMDD in DSM-5 made a statement, he says, that “we were going to take one end of this normal curve, the extreme far right end, and we were going to draw a line and say, those people there have a disease we’re going to label in our book. But if 80 percent of women get some kind of premenstrual symptoms, then it’s normal. And I wondered, if it’s so normal, what could be the reason for it?” © Society for Science & the Public 2000 - 2014.
By NICHOLAS BAKALAR Childhood treatment with human growth hormone is strongly associated with an increased risk for stroke in early adulthood, a new study has found. The study adds evidence to previous reports suggesting an increased cardiac and cerebrovascular risk in children treated with growth hormone. Researchers studied 6,874 children, average age 11, who were small for their age but otherwise generally healthy and were treated with growth hormone from 1985 to 1996. They followed them to an average age of 28. There were 11 strokes in the group, four of them fatal. The analysis found that this was more than twice as many strokes as would be expected in a population this size, a statistically significant difference. The results, published online in the journal Neurology, were particularly striking for hemorrhagic stroke, the type caused by a ruptured blood vessel — there were more than seven times as many as would be expected. The authors acknowledged that they were unable to take into account some risk factors for stroke, such as family history and smoking. “Subjects on growth hormones should not panic on reading these results,” said the senior author, Dr. Joël Coste, a professor of biostatistics and epidemiology at the Hôtel Dieu hospital in Paris. “The doctor prescribing the hormone or the family doctor should be consulted and will be able to inform and advise patients.” © 2014 The New York Times Company
Older people who have a severe vitamin D deficiency have an increased risk of developing dementia, a study has suggested. UK researchers, writing in Neurology, looked at about 1,650 people aged over 65. This is not the first study to suggest a link - but its authors say it is the largest and most robust. However, experts say it is still too early to say elderly people should take vitamin D as a preventative treatment. There are 800,000 people with dementia in the UK with numbers set to rise to more than one million by 2021. Vitamin D comes from foods - such as oily fish, supplements and exposing skin to sunlight. However older people's skin can be less efficient at converting sunlight into Vitamin D, making them more likely to be deficient and reliant on other sources. The international team of researchers, led by Dr David Llewellyn at the University of Exeter Medical School, followed people for six years. All were free from dementia, cardiovascular disease and stroke at the start of the study. At the end of the study they found the 1,169 with good levels of vitamin D had a one in 10 chance of developing dementia. Seventy were severely deficient - and they had around a one in five risk of dementia. 'Delay or even prevent' Dr Llewellyn said: "We expected to find an association between low vitamin D levels and the risk of dementia and Alzheimer's disease, but the results were surprising - we actually found that the association was twice as strong as we anticipated." He said further research was needed to establish if eating vitamin D rich foods such as oily fish - or taking vitamin D supplements - could "delay or even prevent" the onset of Alzheimer's disease and dementia. But Dr Llewellyn added: "We need to be cautious at this early stage and our latest results do not demonstrate that low vitamin D levels cause dementia. BBC © 2014