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StillnessSleep fact

Short naps of about 10 to 20 minutes improve alertness and performance for many people. Because they usually end before deep sleep begins, you are less likely to wake up groggy than after a longer nap.

Sleep science

Health

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The grogginess after waking from deep sleep is called sleep inertia; it usually lasts 15 to 30 minutes but can go on longer. In a 2006 study at Flinders University in Australia, researchers compared afternoon naps of 5, 10, 20 and 30 minutes after a short night's sleep. The 10-minute nap gave the quickest and best boost; the longer naps caused grogginess at first, and their benefits only showed later. In a NASA study of long-haul airline pilots in the early 1990s, pilots given a planned 40-minute rest in the cockpit slept for 26 minutes on average and were more alert later in the flight. Longer naps are not harmful in themselves, but timing matters: a nap late in the afternoon can make it harder to fall asleep at night.

Türkçe oku
Yaklaşık 10-20 dakikalık kısa şekerlemeler birçok kişinin dikkatini toplar ve performansını artırır. Bu kısa uykular çoğunlukla derin uykuya geçmeden bittiği için, uzun bir şekerlemenin ardından gelen sersemlik de pek yaşanmaz.

Derin uykudan uyanınca yaşanan sersemliğe uyku ataleti denir; genellikle 15-30 dakika sürer ama daha uzun da sürebilir. Avustralya'daki Flinders Üniversitesi'nde 2006'da yapılan bir çalışmada, kısa bir gece uykusunun ardından 5, 10, 20 ve 30 dakikalık öğleden sonra şekerlemeleri karşılaştırıldı. En hızlı ve en iyi toparlanmayı 10 dakikalık şekerleme sağladı; daha uzun şekerlemeler önce sersemlik yaptı, yararları ancak sonradan görüldü. NASA'nın 1990'ların başında uzun mesafe uçan havayolu pilotlarıyla yaptığı bir çalışmada, pilotlara kokpitte 40 dakikalık planlı bir dinlenme molası verildi. Pilotlar bu sürede ortalama 26 dakika uyudu ve uçuşun ilerleyen saatlerinde daha dikkatli oldu. Uzun şekerlemeler kendi başına zararlı değildir; ama zamanlama önemlidir: Öğleden sonranın geç saatlerinde uyumak gece uykuya dalmayı zorlaştırabilir.

Sources and further reading

Background reading: Power nap
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He who has health has hope, and he who has hope has everything.

English quotation books have called this an “Arabian proverb” since at least the 1860s; Tryon Edwards's A Dictionary of Thoughts (1891) is one, but these books give no Arabic original, so the label is best taken loosely. The idea is widely shared: good health gives people the strength to plan and to recover from setbacks. Turkish says “Her şeyin başı sağlık”, health comes first, and when a glass breaks people say “Sağlık olsun”: never mind, as long as everyone is well.

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Protein helps with satiety, the feeling of fullness that lasts after a meal. Meals that include beans and lentils, eggs, fish, dairy or other protein sources can help people feel full for longer, although appetite and digestion vary from person to person.

In studies that compare meals with the same number of calories, the higher-protein version usually keeps people satisfied for longer, although the effect is modest. One reason is that protein prompts the gut to release more of the hormone PYY, which tells the brain that food has arrived; a 2006 study led by Rachel Batterham at University College London found the strongest PYY response after high-protein meals. Another is that the body works harder to process protein: a 2004 review by the Maastricht University physiologist Klaas Westerterp reports that digesting and using it burns 20 to 30% of its calories, against 5 to 10% for carbohydrate and up to 3% for fat. UK guidance puts adults' needs at about 0.75 g of protein per kilogram of body weight a day, around 45 g for women and 56 g for men, and average intakes are well above that.

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The fibre we eat comes from plant foods: fruit, vegetables, wholegrains, beans and lentils, nuts and seeds. Meat, fish, eggs and dairy naturally contain none.

Fibre is the part of plant food that our digestive enzymes cannot break down. Much of it comes from the walls of plant cells, which give stems, peel and seeds their structure. Animals do not make these substances, so meat, fish, eggs and milk contain none. Mushrooms, which are fungi rather than plants, also supply a little fibre from their own cell walls. Nutritionists divide fibre into two kinds. Soluble fibre, found in oats, barley, apples and beans, dissolves in water in the gut, can form a gel and helps lower cholesterol. Insoluble fibre, in wholegrains, brown rice, nuts and the skins of fruit and vegetables, adds bulk and helps food pass through. Once fibre reaches the large intestine, gut bacteria ferment part of it into short-chain fatty acids, compounds that feed the cells lining the bowel.

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Whole fruit keeps its fibre and cell structure, so it takes longer to eat and fills you up more than juice. Juicing breaks the cells open and frees their sugars, which are harder on teeth. The NHS therefore counts juice as one of your five daily portions at most, and advises no more than 150ml a day.

In a 2009 study at Pennsylvania State University, Julie Flood-Obbagy and Barbara Rolls gave 58 adults an apple, apple sauce or apple juice 15 minutes before lunch, each with the same weight and calories. After the whole apple, people felt fuller and ate about 15% fewer calories across the starter and lunch together than on days with no starter. Juice did not have that effect, even with the apple's fibre added back. A larger Harvard analysis of about 187,000 American health professionals, published in the BMJ in 2013, found that people who ate more whole fruit, especially blueberries, grapes and apples, were less likely to develop type 2 diabetes, while those who drank more fruit juice were slightly more likely to. Long-term observational studies like this show a link rather than proof of cause, but the two kinds of evidence point the same way.

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Water makes up about 60% of an adult's body weight. The body needs it to control its temperature, keep blood flowing, digest food and keep organs working. When lost fluid is not replaced, thirst can come with tiredness, headache, dizziness and poorer concentration.

Every day we lose water in urine, in sweat and even in our breath, and more in hot weather or during exercise. About a fifth of what we take in comes from food, especially fruit and vegetables, and the rest from drinks. The NHS suggests 6 to 8 glasses of fluid a day, and water, lower-fat milk, tea and coffee all count. Thirst is the body's alarm: when the blood becomes slightly too concentrated, sensors in the hypothalamus, a small region at the base of the brain, trigger the urge to drink. This alarm weakens with age, which is one reason older people become dehydrated more easily. A simple check is the colour of urine: the NHS advises drinking enough to keep it a clear pale yellow, and darker urine is a sign to drink more.

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