8 Facts About Seasonal Affective Disorder

iStock/Martin Dimitrov
iStock/Martin Dimitrov

As the winter days get colder, some look forward to making snow angels and curling up with a mug of hot chocolate. But for millions of people, winter brings debilitating depression and lethargy. Seasonal Affective Disorder (SAD) is thought to affect 6 percent of the U.S. population, with millions more having milder forms of seasonal malaise. Here’s what you need to know about this condition.

1. Seasonal affective disorder is a relatively recent diagnosis.

Doctors have commented on the seasonality of depression in their patients for hundreds of years. The 19th-century psychiatrist Jean-Étienne Esquirol described a Belgian man whose life was generally good, but “at the beginning of autumn [he] became sad, gloomy, and susceptible,” and this pattern had continued for years. Esquirol prescribed a trip to the south of France and then into Italy as winter progressed. In May, the patient returned to Paris “in the enjoyment of excellent health.”

The modern understanding of SAD, however, didn’t emerge until the 1980s. A 1981 article in the Washington Post described a patient who was “almost dysfunctional in the winter, with both her mood and her energy levels at low levels.” It added that Norman Rosenthal, a researcher at the National Institute of Mental Health, “would like to hear from anyone with distinctly seasonal mood disorders. Applicants will be sent questionnaires, from which participants will be selected” for an experimental treatment program.

Decades later, Rosenthal told the Washington Post, “I thought I was dealing with a very rare syndrome. […] We got 3000 responses from all over the country.” In 1984 Rosenthal and colleagues identified SAD in the journal Archives of General Psychiatry, and in 1987 it was added to the American Psychiatric Association’s manual DSM-III-R.

2. Seasonal affective disorder doesn’t just happen in winter.

In the APA's current DSM (DSM-5), one benchmark for diagnosing depressive disorders “with seasonal pattern” is “a regular temporal relationship between the onset of major depressive episodes in major depressive disorder and a particular time of the year (e.g., in the fall or winter).” It also indicates that there must be no seasonally related stressors (such as consistent unemployment in winter), that full remission occurs at “a characteristic time of the year,” and that the pattern has repeated for two years without non-seasonal episodes.

Nothing in that definition requires winter, however. An estimated 10 percent of people with SAD experience the opposite of the conventional diagnosis—their depression appears in spring and summer. And in places like the Philippines, studies have found more people feel their worst in summer rather than in winter [PDF].

According to the National Institute of Mental Health, summer-onset and winter-onset SAD can even have different symptoms. Winter symptoms can include oversleeping, weight gain, carbohydrate cravings, and low energy, while summer symptoms might be poor appetite, insomnia, agitation, anxiety, and even violent behavior.

3. It’s also not the ‘winter blues.’

SAD is not the same as feeling a little down as it gets gloomy outside. A SAD diagnosis meets all the criteria for major depression and should be treated as seriously—the only difference is that SAD has a seasonal pattern. Psychiatrists do recognize ‘winter blues,’ or sub-syndromal SAD (S-SAD), for “individuals who do not meet diagnostic criteria for depression during the fall/winter months, but who experience mild to moderate symptoms during fall or winter,” SAD expert Kelly Rohan told the APA. This form may affect an additional 15 percent of the US population. (This number is highly dependent on where the S-SAD patients live, however.)

4. Your chance of experiencing SAD depends on your latitude (to a point).

It might seem obvious that as you get further north—to regions with colder, darker, and longer winters—SAD would be more prevalent. There is some evidence for this: An estimated 1 percent of Floridians experience SAD compared to 9 percent of Alaskans. But one study in Tromsø, in northern Norway, found “no significant differences in the reporting of current mental distress depending on season” (although they did find people had more sleeping problems in winter). Icelanders also have remarkably low instances of SAD. Even more surprisingly, people of Icelandic descent living in Canada have a lower prevalence of SAD than non-Icelandic Canadians in the same area [PDF].

5. Not everyone in a region is affected the same way.

SAD is reported to affect four times as many women as men, and a recent pilot study indicated vegetarianism may also be associated with SAD. The researchers found that:

“The percentage of SAD patients among Finnish vegetarians was four times higher than in the normal population. The percentage of vegetarians among the SAD patients in a Dutch outpatient clinic was three times higher than in the normal population. In the Dutch population, the seasonal loss of energy, in particular, is related to vegetarianism.”

Some factors may confound the data (for example, it’s possible vegetarians are more likely to forgo antidepressants, so there are more of them in outpatient facilities), but the researchers say the findings suggest a link. In fact, one theory for Iceland’s low SAD rate suggests that Icelanders’ fish-heavy diet may have a protective effect (and Icelanders living in Canada might be sticking with their traditional foods).

6. We don’t know what causes seasonal affective disorder.

While scientists haven’t figured out what factors cause SAD, the most popular theory is the phase shift hypothesis: That, due to later sunrises and earlier sunsets, the body’s circadian rhythms sometimes get out of whack with its sleep/wake cycles, like a several-months-long jet lag. It’s also possible that people with winter SAD can’t regulate serotonin or they overproduce melatonin, and the imbalance alters circadian rhythms.

7. Luckily, seasonal affective disorder is treatable.

For years, the gold standard of SAD treatment has been light therapy. The process involves sitting near a light box for around 30 minutes after you wake up. Your eyes are open, but not looking directly at the light, meaning the therapy can be done while watching TV, reading a newspaper, or having breakfast.

But researchers warn again self-treating with light therapy—it can negatively affect people with bipolar disorder or eye problems. And, light boxes must be made specifically for treating SAD. Many commercially available light boxes release predominantly UV light, and SAD boxes should release as little UV as possible.

More recently, research has been looking into Cognitive Behavioral Therapy (CBT)—a technique that alters negative thoughts to manipulate emotions and behaviors, like changing your thinking from “I hate winter” to “I prefer summer.” With CBT, some researchers have seen fewer recurrences, less-severe symptoms, and higher remissions compared to light therapy users. Antidepressants are also prescribed for SAD.

8. SAD may have once been an evolutionary advantage.

In the 1981 Washington Post article, the SAD sufferer commented that she “should have been a bear” because “bears are allowed to hibernate, and people aren’t.” As the years went on, some proposed that the symptoms of winter SAD—sleeping more, being less active, and eating fattening foods—could be a vestigial hibernation instinct. Many dismissed that explanation, but in the early 2000s things began to change. A Russian study found that women without depression and with non-seasonal depression consumed around the same amount of oxygen, while women with winter depression consumed less [PDF]. Doctors began to think SAD exists today because it once offered some evolutionary benefit for humans surviving winter.

One proposed benefit is reproduction. People with winter SAD are lethargic in winter but generally active in spring and summer, which increases the probability of procreation in those seasons. If a child is conceived between May and September, that means a high probability of being born between February and June, which some researchers propose would increase chances of survival before winter kicks in. Meanwhile, Robert Levitan at the University of Toronto “consider[s] SAD to be an evolutionary disorder, an energy-conserving process that is no longer helpful in modern society. While in modern times it’s not good for us to slow down too much in the winter, or to gain lots of weight, this probably helped our ancestors survive in the ice age.”

7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.

9 Surprising Facts About the Scientific Study of Sex

vadimguzhva/iStock via Getty Images
vadimguzhva/iStock via Getty Images

The scientific study of sex is much more exciting than an awkward sex ed class. While writing my book Sex Weird-o-Pedia, these were some of the most interesting facts about science and sex that I came across.

1. Some sex researchers didn't want their findings to get into the wrong hands.

The pioneering sex researcher Richard von Krafft-Ebing didn’t want his knowledge in the hands of ordinary folk. So he wrote Psychopathia Sexualis, the founding document of modern sexology—which was published in Germany in 1886 then translated and published in English in 1939—in Latin to discourage regular Joes (and/or Janes) from reading it.

2. You burn more calories mowing the lawn than you do having sex.

Young woman poses for selfie while mowing the lawn
Alina Rosanova/iStock via Getty Images

Sex might seem strenuous when things get hot and heavy, but it's usually not that great of a workout. You'd have to go at it for nearly 200 minutes to burn as much energy having sex as you do during a 30-minute run. Even mowing the lawn burns about three times more calories than sex. According to the British Heart Foundation, sex burns about the same amount of energy per minute as ironing clothes.

3. A surprising number of mothers claim to be virgins.

In a 2013 study of several thousand pregnant women in the U.S. published by BMJ, about 1 percent of the participants claimed they were virgins when they gave birth. This, of course, calls into question the veracity of studies that rely on self-reported sexual behaviors.

4. Penicillin may have ignited the sexual revolution.

One economist says that penicillin, and not the birth control pill, was the real enabler of the sexual revolution. A study published in the Archives of Sexual Behavior in 2013 shows that penicillin contributed to a 75 percent decline in the number of deaths caused by syphilis from 1947 to 1957. Since the new treatment made sex safer, people started having riskier sex, which resulted in increases in the numbers of children born out of wedlock and teenage pregnancies.

5. Twins can have different dads.

A photo of fraternal twins
Aleksandr Zhurilo/iStock via Getty Images

While it is very rare, it is possible for fraternal twins to have two different fathers. What’s more common is for a rom-com to be based on this scenario.

6. Gender may influence how people handle sexual jealousy.

Research from evolutionary psychologists indicates that people’s gender influences how they react to sexual jealousy. For men, they react more strongly to sexual unfaithfulness than emotional infidelity. For women, it is the reverse. The theory behind these behaviors comes back to evolution: Males who were intolerant toward their wives becoming sexually active with other men were less likely to become an object of derision and more likely to see their own genes pass onto future generations. Women who prevented their husbands from emotionally bonding with other women reduced the chances of the men spending their resources on other women.

7. One of Ivan Pavlov's colleagues created his own (slightly x-rated) conditioning experiment with dogs.

You’re probably aware of Russian researcher Ivan Pavlov and his famous conditioning experiment in which he trained a dog to salivate at the sound of a bell. What you might not know is that one of Pavlov’s American students, W. Horsley Gantt, conditioned dogs to become sexually aroused when they heard specific tones. The experiment, according to Mandy Merck's In Your Face: 9 Sexual Studies, was intended "to study conflicts of the drives between ... experimentally induced anxiety states and sexual excitement."

8. Couples whose first child is a girl are more likely to get divorced.

Parents pay attention to their phones instead of their daughter
grinvalds/iStock via Getty Images

Married couples whose first child is a girl are more likely to get divorced than those whose first child is a boy. Scientists are split as to why this is. One theory is that female embryos are better able to endure maternal stress than male embryos, so pregnant women in unhappy marriages are less likely to have a miscarriage if the child they are bearing is a girl. But once they have a daughter, these couples are more likely to split up since there were already fissures in their relationship prior to the child’s birth.

9. There's a link between pubic hair and STIs.

A downside of pubic grooming is that it might raise STI risk. In a study conducted by a University of Texas scholar, people who regularly shaved their pubic areas contracted STIs about 80 percent more often than those who never shaved down there. One suggestion is that those who regularly shave are more likely to tear their skin, making it easier for viruses to enter the body.

Ross Benes is the author of Sex Weird-o-Pedia: The Ultimate Book of Shocking, Scandalous, and Incredibly Bizarre Sex Facts.

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