Twenty-five people sat in a room for a little over four hours while the fresh air was turned down. Nothing else changed. By the end they reported more headache, more tiredness and more trouble thinking clearly, and they were slower at simple sums. Then the test was run again with the fresh air back on and pure carbon dioxide pumped in to the same level. Nothing happened.
So the fog that settles on a meeting after lunch is real, and it belongs to the room. Stale air made by the people in it does the damage, and a window undoes it.
That is the kind of energy remedy worth having: little known, cheap and tested.
The internet is full of the other kind, the ones that arrive with a confident number and no source. Mouth breathing "wastes 20% of your energy". A pinch of skin "reveals cellular dehydration".
Each remedy below has been checked against the evidence. Some hold. Some hold a little. A few came from nowhere.
1. Open a window
That stuffy conference room where everyone gets sleepy after half an hour? Blame the air before you blame the speaker.
The test in the opening was the second of its kind. In an earlier one, 22 people worked through a decision-making test at three levels of carbon dioxide. At the level an ordinary full room reaches, their scores fell on six of nine measures. At the level of a badly aired one, they fell hard on seven.
Those two tests disagree about the culprit. One blames the gas itself, the other blames everything else people give off along with it. They agree about the cure.
The bedroom counts double. Thirty students slept for a week with the bedroom aired, by an open window or a quiet fan in the vent, and for a week without. With the fresh air they slept better, felt less sleepy the next day and did better on a test of logical thinking. With the window shut, their bedrooms averaged about 2,500 parts per million of carbon dioxide overnight, three to four times the level with it open, and about the level at which the decision-makers' scores fell hard.
And before you buy a plant for the job: house plants do clean the air inside small sealed test chambers. In a room it is another story. Going by 196 chamber results, it would take between 10 and 1,000 plants on every square metre of floor to match what ordinary ventilation already does.
The word knows what the thing is for. "Window" comes from the Old Norse vindauga: wind-eye. It was a hole for air before it was a thing to look through. Florence Nightingale made it the first rule of nursing: "To keep the air he breathes as pure as the external air, without chilling him."
One warning. Headaches, dizziness and tiredness that ease when you leave the house can be carbon monoxide from a faulty boiler, cooker or fire, and an alarm in each room with one of those costs little.
Verdict. Holds.
Open a window or a door for two minutes and notice what happens to your head. If you feel sharper outdoors than indoors at the same temperature, your indoor air is the suspect. At night, leave the bedroom window or door ajar.
2. Cool the room
During a heat wave, 44 students took two short thinking tests every day. Twenty-four lived in air-conditioned rooms at about 21°C (70°F). Twenty lived in rooms without it, at about 26°C (79°F). The ones in the warm rooms reacted 13% more slowly.
A warm afternoon makes you slow, and slow feels like tired.
Nights follow the same rule. In real beds, under bedding, heat means more waking and less deep sleep. Cold does not disturb sleep the same way, so long as the bedding is up to it.
Verdict. Holds.
On a hot afternoon, deal with the room before you reach for a coffee. Shade the window, open another, move the fan. At night, err on the cool side.
3. Make the days bright
You need bright days and dark nights. Indoor light is neither.
Thirty-two volunteers spent an hour at a desk under ordinary office light or under light five times as bright. Under the bright light they felt less sleepy and more energetic, and their reactions were faster. The lift in how they felt came in the morning and in the afternoon alike.
Windows do the same job for nothing. Among 49 office workers, those with no window near them scored lower on vitality and slept worse. The ones with windows got more light across the working week and slept longer.
The sky does it with no desk at all. An overcast day gives about 1,000 lux, the unit of brightness. That is two to three times a lit office, and the same as the bright desk in that test. Step outside under cloud and you are already there.
Darkness is the other half. People who read on a light-emitting screen in the hours before bed took longer to fall asleep, made less melatonin, the hormone of darkness, and were less alert the next morning than when they read a printed book.
Two things sold alongside this have nothing comparable behind them: a special "afternoon window" for light, and red-light panels for the evening.
Verdict. Daylight holds. The gadgets can wait.
Take the desk by the window, take the next phone call outside, and at night read on paper.
4. Breathe through your nose
Your nose is air-conditioning equipment. It warms or cools incoming air to within a degree of body temperature, adds moisture and filters out dust. Your mouth does none of that.
The nose also makes a gas. The sinuses produce nitric oxide, which widens blood vessels, and a breath taken through the nose carries it down to the lungs. In six of eight healthy volunteers, oxygen measured through the skin read 10% higher while they breathed through the nose than while they breathed through the mouth.
Humming turns it up. In ten volunteers, humming raised the nitric oxide in the nose fifteen-fold. Yoga has a humming breath of its own, named Bhramari: "like a bee".
Now the claims. The line that mouth breathing "wastes 20% of your energy" has no traceable source, and neither does its cousin about carrying an extra 20 pounds. And taping your mouth shut at night, the trick the internet loves? Reviewers pulled together 10 small sets of findings on 213 people. Two showed a benefit for breathing during sleep. The rest showed none, and the reviewers warned of suffocation where the nose is blocked.
Verdict. The nose holds, in a small way. The tape fails.
Hum with your mouth closed for a minute. If that is hard work, your nose is blocked. A salt-water rinse is the first thing to try, and a comes with the bottle and the sachets. A nose that stays blocked wants looking at before anything else on this list.
5. End the shower cold
Cold is a real lever, and a smaller one than the stunts on social media suggest. The stunts are older than social media, mind. In 1886 a Bavarian priest, Sebastian Kneipp, published My Water Cure, with its "ice cold baths and walking barefoot in the snow". Within seven years a critic was calling his cures "dangerous in most cases".
In the Netherlands, 3,018 adults either showered as usual or ended every shower with a burst of cold water for a month. Over three months the cold-shower groups took 29% fewer days off sick. The benefit they mentioned most was more energy.
Regular cold also changes the body. After ten days of spells in a cool room, volunteers had more active brown fat, the kind that burns fuel to make heat. They shivered less and judged the same room warmer.
What has never been shown in people is the promise that cold showers "grow new mitochondria". Leave that on the poster.
Only people without serious illness were tested. If you have a heart condition, leave this one out.
Verdict. Holds, modestly.
Start small. End tomorrow's shower with a short cold burst and see how the next hour feels.
6. Drink water, and skip the folklore
A small shortfall of water does cost you. When 25 young women lost just over 1% of their body weight in water, their mood dropped, tasks felt harder, their concentration slipped and headaches came on.
The rituals built on top of that are another matter. Pinch the back of your hand to detect "cellular dehydration". Salt your first glass of the day. Avoid ice water because it "costs energy". None of it has a finding behind it. When reviewers checked 67 quick signs and tests for dehydration in older people, only three showed any ability to pick it out, none did so reliably, and their advice was to trust no single sign.
Verdict. Water holds. The rituals fail.
Drink when you are thirsty and with every meal. 7 Fun and Tasty Ways to Stay Hydrated Without the Boredom has the rest.
7. Time your minerals, where timing is real
Supplement schedules are mostly decoration. Four things in them are true.
The form of magnesium matters. Magnesium oxide, the cheap form, is essentially chalk. In volunteers it was absorbed at about 4%. Other forms did far better. If you take magnesium, carries NSF's contents certification, which means an outside lab checked the bottle against the label. Failing kidneys struggle to clear magnesium, so with kidney disease have it checked before you take any.
Iron absorbs better with gaps. Forty women who were low in iron took it either every day or every other day. On alternate days they absorbed about 22% of what they took, against 16%.
Coffee and tea get in the way. A cup of coffee with a meal cut the iron absorbed from it by 39%. Tea cut it by 64%. Coffee an hour before the meal made no difference. Coffee an hour after did the same damage as coffee with it. Calcium does something similar: in 126 people, the calcium in a small glass of milk cut the iron absorbed from a meal by half or more.
Meat is the iron that gets in. Meat, fish and poultry carry haem iron, which the body absorbs better than the iron in plants and fortified flour. Lean meat and seafood are its richest sources. A low-carb, keto or carnivore plate has that covered.
One more truth sits under all of this. Iron lifts tiredness when your stores are low, and only then. Tired women with low iron stores but normal blood counts felt their fatigue drop by almost half over twelve weeks of iron, against under a third on a dummy pill. The people most likely to run low are women with heavy periods, pregnant women, frequent blood donors and small children. A blood test for ferritin, your iron stores, tells you where you stand. Iron is one to test for, never to guess at: too much does harm, and a large amount can kill a child, so keep the bottle out of reach.
Verdict. Form and spacing hold. The rest of the timetable fails.
Keep coffee and tea well away from the meal that carries your iron.
8. Write it down
The idea that every decision drains a tank of willpower, glucose and all, had a good run. Then 23 labs ran the classic test of that tank again with 2,141 people between them, and the effect all but disappeared.
Its most famous exhibit is a set of parole judges. Their favourable rulings fell from about 65% to nearly zero through each session and jumped back after every food break. The finding gave new life to an old jibe, that justice is "what the judge ate for breakfast". The numbers are real. The reading is disputed, because the order of cases was never random: prisoners without a lawyer tended to be heard last.
What does hold is smaller and more useful. Unfinished tasks intrude on whatever you do next. When people were allowed to make a specific plan for the unfinished task, the intrusion stopped.
It works at bedtime too. Fifty-seven young adults spent five minutes before bed writing either a to-do list for the coming days or a list of what they had already done. The to-do group fell asleep faster, and the more specific the list, the faster.
Verdict. The tank fails. The list holds.
Write down everything you are mentally tracking right now, and put one next step beside each item. Do it again before bed.
9. B vitamins and CoQ10
CoQ10 is a compound your cells use in making energy, sold as a supplement. Across 13 tests and 1,126 people, those taking it reported less fatigue than those on a dummy pill. The effect was small to moderate, and it showed up in healthy people and ill ones. It can interfere with warfarin and with insulin, so check before you take it alongside either.
B vitamins are simpler. Tiredness is a sign of running short of B12, and topping up helps people who are short. That is about 6% of people under 60 and about 20% of those over it, and metformin, the common diabetes tablet, and long-term acid-reducing tablets pull B12 down. For everyone else there is nothing to top up.
Verdict. CoQ10 has some support. B vitamins hold only if you are low.
Test before you buy. Nutrient Deficiencies: Who's at Risk and Which Test to Get covers which tests to ask for.
10. Coffee
This one needs no introduction, which is the problem. Coffee is the energy remedy already in your hand.
In daily drinkers, the morning cup mostly undoes the tiredness and low mood that a night without caffeine has built. It returns you to where a person who never drinks it started the day. The bill arrives at night: a strong coffee taken six hours before bed still cut people's sleep by more than an hour, and they were unaware of it. With a meal, as remedy 7 showed, it takes iron with it.
Verdict. Borrowed, and paid back with interest.
Drop the afternoon cup first. If it's the cup you'd miss, is roasted chicory with no caffeine in it. How to Quit Coffee: Getting Through Caffeine Withdrawal covers the rest.
Three more that came from nowhere
Switching sides in bed to "drain" the brain. The finding behind it comes from rats under anaesthetic, which cleared waste from the brain faster lying on their sides. Nobody has shown that turning over at half-time does anything for a person.
Six hours of "deep" sleep that beat eight. A number without a test.
The habit that must start at a set hour of the day. The same.
When it's something else
Everything above is for ordinary tiredness. If yours has gone on for weeks with no cause you can name, look for one.
Some causes are plain enough: pregnancy, the menopause, getting over an illness such as glandular fever, and some medicines. Others leave clues. Loud snoring with gasping or choking at night points to sleep apnoea, where breathing keeps stopping during sleep. Pale skin, breathlessness and a heartbeat you can feel point to low iron. Great thirst and frequent trips to the toilet point to diabetes. Tiredness that comes with restlessness, nerves and irritability points to an overactive thyroid.
Where to start
Start with the surroundings, because they cost nothing and they work on everyone in the room. Then the nose. Then water and the minerals. Leave the cold for last, since it asks the most of you.
Test one change at a time and give it two weeks before you add another. Try five at once and you will never know which one did the work. Meals and the ten-minute nap have an article of their own: 5 Ways to Harness Your Energy and Beat the Afternoon Slump.
The 25 people in the stale room needed no supplement and no gadget. They needed a window. The boring, unsexy daily practice is the whole trick.
Reading this changes nothing. Which person will you be? Pick one remedy and keep it for 30 days. Start with the window.
Is the room fine and the tiredness still there? Unstoppable Energy: 14 Ways to Stay Focused and Strong Every Day — how your brain reads effort, and fourteen ways to change the reading.
Sleeping enough and still worn out? Why You're Always Tired: The Rest You're Missing — the rest that sleep, workouts and clean eating leave out, and how to get it.
Know someone who buys a new supplement every time they feel tired? Send them this, and open their window while you're there.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional. If your mood has been low for weeks or you're having thoughts of harming yourself, reach out for help today.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
Sources
Zhang X, Wargocki P, Lian Z, Thyregod C (2017). Effects of exposure to carbon dioxide and bioeffluents on perceived air quality, self-assessed acute health symptoms, and cognitive performance. Indoor Air 27(1):47–64. doi.org/10.1111/ina.12284
Satish U, Mendell MJ, Shekhar K, et al. (2012). Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2 Concentrations on Human Decision-Making Performance. Environmental Health Perspectives 120(12):1671–1677. doi.org/10.1289/ehp.1104789
Strøm-Tejsen P, Zukowska D, Wargocki P, Wyon DP (2016). The effects of bedroom air quality on sleep and next-day performance. Indoor Air 26(5):679–686. doi.org/10.1111/ina.12254
Cummings BE, Waring MS (2020). Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies. Journal of Exposure Science & Environmental Epidemiology 30(2):253–261. doi.org/10.1038/s41370-019-0175-9
Wiktionary. window. en.wiktionary.org
Nightingale F. Notes on Nursing: What It Is, and What It Is Not, Chapter I. en.wikisource.org
NHS. Carbon monoxide poisoning. nhs.uk
Cedeño Laurent JG, Williams A, Oulhote Y, et al. (2018). Reduced cognitive function during a heat wave among residents of non-air-conditioned buildings: An observational study of young adults in the summer of 2016. PLOS Medicine 15(7):e1002605. doi.org/10.1371/journal.pmed.1002605
Okamoto-Mizuno K, Mizuno K (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology 31:14. doi.org/10.1186/1880-6805-31-14
Smolders KCHJ, de Kort YAW, Cluitmans PJM (2012). A higher illuminance induces alertness even during office hours: Findings on subjective measures, task performance and heart rate measures. Physiology & Behavior 107(1):7–16. doi.org/10.1016/j.physbeh.2012.04.028
Boubekri M, Cheung IN, Reid KJ, Wang CH, Zee PC (2014). Impact of Windows and Daylight Exposure on Overall Health and Sleep Quality of Office Workers: A Case-Control Pilot Study. Journal of Clinical Sleep Medicine 10(6):603–611. doi.org/10.5664/jcsm.3780
Wikipedia. Lux. en.wikipedia.org
Chang AM, Aeschbach D, Duffy JF, Czeisler CA (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences 112(4):1232–1237. doi.org/10.1073/pnas.1418490112
Wikipedia. Nasal cavity. en.wikipedia.org
Lundberg JON, Settergren G, Gelinder S, et al. (1996). Inhalation of nasally derived nitric oxide modulates pulmonary function in humans. Acta Physiologica Scandinavica 158(4):343–347. doi.org/10.1046/j.1365-201X.1996.557321000.x
Weitzberg E, Lundberg JON (2002). Humming Greatly Increases Nasal Nitric Oxide. American Journal of Respiratory and Critical Care Medicine 166(2):144–145. doi.org/10.1164/rccm.200202-138BC
Wikipedia. Bhramari. en.wikipedia.org
Rhee J, Iansavitchene A, Mannala S, Graham ME, Rotenberg B (2025). Breaking social media fads and uncovering the safety and efficacy of mouth taping in patients with mouth breathing, sleep disordered breathing, or obstructive sleep apnea: A systematic review. PLOS One 20(5):e0323643. doi.org/10.1371/journal.pone.0323643
NHS. Catarrh. nhs.uk
Wikipedia. Sebastian Kneipp. en.wikipedia.org
Buijze GA, Sierevelt IN, van der Heijden BCJM, Dijkgraaf MG, Frings-Dresen MHW (2016). The effect of cold showering on health and work: a randomized controlled trial. PLoS One 11(9):e0161749. doi.org/10.1371/journal.pone.0161749
van der Lans AAJJ, Hoeks J, Brans B, et al. (2013). Cold acclimation recruits human brown fat and increases nonshivering thermogenesis. Journal of Clinical Investigation 123(8):3395–3403. doi.org/10.1172/JCI68993
Armstrong LE, Ganio MS, Casa DJ, et al. (2012). Mild dehydration affects mood in healthy young women. The Journal of Nutrition 142(2):382–388. doi.org/10.3945/jn.111.142000
Hooper L, Abdelhamid A, Attreed NJ, et al. (2015). Clinical symptoms, signs and tests for identification of impending and current water-loss dehydration in older people. Cochrane Database of Systematic Reviews (4):CD009647. doi.org/10.1002/14651858.CD009647.pub2
Firoz M, Graber M (2001). Bioavailability of US commercial magnesium preparations. Magnesium Research 14(4):257–262. pubmed.ncbi.nlm.nih.gov
Wikipedia. Magnesium. en.wikipedia.org
Stoffel NU, Cercamondi CI, Brittenham G, et al. (2017). Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. The Lancet Haematology 4(11):e524–e533. doi.org/10.1016/S2352-3026(17)30182-5
Morck TA, Lynch SR, Cook JD (1983). Inhibition of food iron absorption by coffee. The American Journal of Clinical Nutrition 37(3):416–420. doi.org/10.1093/ajcn/37.3.416
Hallberg L, Brune M, Erlandsson M, Sandberg AS, Rossander-Hultén L (1991). Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. The American Journal of Clinical Nutrition 53(1):112–119. doi.org/10.1093/ajcn/53.1.112
National Institutes of Health, Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals. ods.od.nih.gov
Vaucher P, Druais PL, Waldvogel S, Favrat B (2012). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. Canadian Medical Association Journal 184(11):1247–1254. doi.org/10.1503/cmaj.110950
NHS. Iron. nhs.uk
Hagger MS, Chatzisarantis NLD, Alberts H, et al. (2016). A multilab preregistered replication of the ego-depletion effect. Perspectives on Psychological Science 11(4):546–573. doi.org/10.1177/1745691616652873
Danziger S, Levav J, Avnaim-Pesso L (2011). Extraneous factors in judicial decisions. Proceedings of the National Academy of Sciences 108(17):6889–6892. doi.org/10.1073/pnas.1018033108
Wikipedia. Hungry judge effect. en.wikipedia.org
Masicampo EJ, Baumeister RF (2011). Consider it done! Plan making can eliminate the cognitive effects of unfulfilled goals. Journal of Personality and Social Psychology 101(4):667–683. doi.org/10.1037/a0024192
Scullin MK, Krueger ML, Ballard HK, Pruett N, Bliwise DL (2018). The effects of bedtime writing on difficulty falling asleep: A polysomnographic study comparing to-do lists and completed activity lists. Journal of Experimental Psychology: General 147(1):139–146. doi.org/10.1037/xge0000374
Tsai IC, Hsu CW, Chang CH, Tseng PT, Chang KV (2022). Effectiveness of Coenzyme Q10 Supplementation for Reducing Fatigue: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Frontiers in Pharmacology 13:883251. doi.org/10.3389/fphar.2022.883251
National Center for Complementary and Integrative Health. Coenzyme Q10. nccih.nih.gov
NHS. Vitamin B12 or folate deficiency anaemia: symptoms. nhs.uk
Wikipedia. Vitamin B12 deficiency. en.wikipedia.org
NHS. Metformin. nhs.uk
NHS. Omeprazole. nhs.uk
James JE, Rogers PJ (2005). Effects of caffeine on performance and mood: withdrawal reversal is the most plausible explanation. Psychopharmacology 182(1):1–8. doi.org/10.1007/s00213-005-0084-6
Drake C, Roehrs T, Shambroom J, Roth T (2013). Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. Journal of Clinical Sleep Medicine 9(11):1195–1200. doi.org/10.5664/jcsm.3170
Lee H, Xie L, Yu M, et al. (2015). The Effect of Body Posture on Brain Glymphatic Transport. Journal of Neuroscience 35(31):11034–11044. doi.org/10.1523/JNEUROSCI.1625-15.2015
NHS. Tiredness and fatigue. nhs.uk