General Knowledge

How Long Can Humans Hold Their Breath? As the Daily Mail explains, humans set breath-holding records in water because they “can hold their breath twice as long underwater they can on land.” The reason: the “diving reflex,” in which the body slows its heart rate and metabolism in order to conserve oxygen and energy when submerged in cold water. The pulse rate in an untrained diver, the Daily Mail says, will decrease 10 to 30 percent when underwater. But professional divers can reduce theirs by more than 50 percent. Which brings us to records. The event in question—holding one’s breath underwater for as long as possible without moving—is officially called “static apnea,” and there are two ways static apnea records are kept: for dives performed after breathing in pure oxygen, and for dives performed without pure oxygen. The Guinness Book of World Records allows divers to hyperventilate for up to 30 minutes with pure oxygen before they submerge for their record attempt. This prac...

Vitamin C Vitamin C burst into prominence back in the 1970s, when Nobel Prize-winning scientist Linus Pauling claimed that high doses could stop cancer and might be the long-sought cure for the common cold. Alas, neither claim has quite held up under scrutiny. Vitamin C doesn't prevent colds. Nor does taking large doses slow or stop cancer. But Pauling's instincts were not entirely wrong. There are still many sound reasons to get plenty of C. What It Does ? Researchers have long known that vitamin C is an essential building block of collagen, the structural material for bone, skin, blood vessels and other tissue. Failing to get enough vitamin C causes inflammation of the gums, scaly skin, nosebleed, painful joints and other problems associated with scurvy. In addition, many studies show that eating foods rich in C can reduce the risk of developing cancer, particularly cancers that strike the mouth and digestive tract, according to Jane Higdon, a nutrition scienti...

Surprising Health Benefits of B Vitamins Good nutrition is tied to good health, as well as to the prevention and treatment of many conditions. Getting the recommended amounts of vitamins each day is an important part of the nutrition equation, and B vitamins are essential for preventive care. Abundant in green vegetables, whole or enriched grains, dairy, and meats, B vitamins help promote a healthy metabolism and are also linked to a reduced risk of stroke, research shows. Take vitamin B12, for example. According to the Mayo Clinic, vitamin B12, a water-soluble vitamin, plays a significant role in nerve function, the formation of red blood cells, and the production of DNA. While most people get plenty of vitamin B12 benefits in a varied, balanced diet, if you are on a vegan or vegetarian diet, you are at risk for vitamin B12 deficiency. Also, elderly adults and people with GI disorders lack adequate B12. Signs of vitamin B12 deficiency include Anemia Confusion Dementia ...

Vitamin A Vitamin A, along with other vitamins, minerals and other compounds, is an essential micronutrient. This means that our bodies cannot manufacture it and therefore it has to be included in our diet. Vitamin A from food is stored in the liver until required by the body and is bound to protein before being transported to where it is needed. Vitamin A is essential for many physiological processes, including maintaining the integrity and function of all surface tissues (epithelia): for example, the skin, the lining of the respiratory tract, the gut, the bladder, the inner ear and the eye. Vitamin A supports the daily replacement of skin cells and ensures that tissues such as the conjunctiva are able to produce mucous and provide a barrier to infection. Vitamin A is also essential for vision under conditions of poor lighting, for maintaining a healthy immune system, for growth and development and for reproduction. Vitamin A supports many systems in the body. For this reas...

Causes and Symptoms of Vitamin D Deficiency Vitamin D is an extremely important vitamin that has powerful effects on several systems throughout your body (1Trusted Source). Unlike other vitamins, vitamin D functions like a hormone, and every single cell in your body has a receptor for it. Your body makes it from cholesterol when your skin is exposed to sunlight. It's also found in certain foods such as fatty fish and fortified dairy products, though it's very difficult to get enough from diet alone. The recommended daily intake (RDI) is usually around 400–800 IU, but many experts say you should get even more than that. Vitamin D deficiency is very common. It's estimated that about 1 billion people worldwide have low levels of the vitamin in their blood (2Trusted Source). According to a 2011 study, 41.6% of adults in the US are deficient. This number goes up to 69.2% in Hispanics and 82.1% in African-Americans (3Trusted Source). Here are 7 common risk facto...

Thai Elephant Eat in a Day Jay Simpson is a Digital Storyteller and National Geographic Young Explorer researching our relationship with wildlife and interventions in human-wildlife conflicts. This story comes from Thailand, during a trip exploring ecotourism and wildlife that was completed in collaboration with Rafa Salvador. Read more of Jay’s stories and follow him on Instagram and Twitter. If you... Jay Simpson is a Digital Storyteller and National Geographic Young Explorer researching our relationship with wildlife and interventions in human-wildlife conflicts. This story comes from Thailand, during a trip exploring ecotourism and wildlife that was completed in collaboration with Rafa Salvador. Read more of Jay’s stories and follow him on Instagram and Twitter. An elephant takes in a meal at Elephant’s World. (Photo by Jay Simpson. If you love elephants, traveling to Thailand can take you up-close and personal with the objects of your affection. The elephants here are d...

How Long Can a Person Survive without Food? The duration of survival without food is greatly influenced by factors such as body weight, genetic variation, other health considerations and, most importantly, the presence or absence of dehydration. For total starvation in healthy individuals receiving adequate hydration, reliable data on survival are hard to obtain. At the age of 74 and already slight of build, Mahatma Gandhi, the famous nonviolent campaigner for India's independence, survived 21 days of total starvation while only allowing himself sips of water. In a 1997 article in the British Medical Journal, Michael Peel, senior medical examiner at the Medical Foundation for the Care of Victims of Torture, cites well-documented studies reporting survivals of other hunger strikers for 28, 36, 38 and 40 days. Most other reports of long-term survival of total starvation, however, have been poorly substantiated. [Editor's Note: Reports of the 1981 hunger strike by politica...