Of all things we'd like more of - time, sleep, cake icing - energy is top of most of our lists. For almost all of us, energy levels swirl down the day's drain as more hours pass. Slowly leaking. Until. We. Finally. Crash. Sometimes, we don't know what makes us tired, whether it's too much stress or too little sleep, exercise or sunlight. But we know the cures - and they're in the form of what you drink, eat and pop. Here, a guide to big myths about energy boosters, and how to power on with juice to spare.

MYTH: Sweets give you a sugar high but then comes the crash.

If you're sluggish at 4pm, conventional wisdom says you're hypoglycemic. Your blood sugar's low, and some M&Ms will make those levels spike then plunge. But that line of thinking has as much truth as the Loch Ness legend, without even a grainy photo to back it up.

"There's no evidence to support the idea that mid-afternoon tiredness is caused by hypoglycemia, or that healthy people feel normal fluctuations in blood sugar," says endocrinologist Dr Phillip Cryer. "The threshold for symptoms of low blood sugar is 50 to 55mg of glucose per deciliter [100ml] of blood, and it's very, very rare for a healthy person to get to those levels."

Rather than being low on blood sugar, you're low on serotonin - the brain chemical that makes you feel focused, attentive and energetic, says Dr Judith Wurtman, author of The Serotonin Diet.

Instead of the celery sticks: Bring back the carbohydrates. Carbs become glucose in your bloodstream, and as insulin goes to work on the glucose, it starts a chain of chemical events: an amino acid called tryptophan travels to the brain and converts to serotonin to keep your energy up. Dr Wurtman goes against the rest of the pack by recommending snacks that are almost pure carbs - so vending machine pretzels or licorice aren't necessarily off-limits anymore.

Still, you're better off with carbs that give you nutritional bang for your buck - a piece of fruit or a couple of handfuls of fat-free popcorn will keep serotonin levels up without doing the same for kilojoule counts. "You'll be more attentive to what you're doing and feel you can take on more tasks," Dr Wurtman says. "It's not that you'll feel extremely energetic - you won't get that no matter what you eat. But you'll lose the desperate feeling of tiredness."

MYTH: High-dose vitamins up energy levels

At health stores you'll see lots of bottles with this promise: "Increased Energy!" In reality, most of these supplements are high concentrations of B vitamins or iron.

B vitamins help release energy from food; if deficient you will feel tired. "Very few of us are deficient in B vitamins - they're easy to get. No research supports the idea that high doses of Bs do you any good when it comes to energy," says nutritionist Connie Diekman.

"If you're not deficient, adding B vitamins won't do anything. Most Bs are water-soluble, and your body takes what it needs and pees out the rest." Which means that you could literally be pissing away your money.

While iron carries oxygen through your blood, that doesn't mean more iron equals more oxygen. "For most of us, the odds that ordinary afternoon tiredness is from iron deficiency are slim," Diekman says. "If you're deficient, you're tired throughout the day, you feel weak and you're easily winded."

Those likely to be iron-deficient are four to eight per cent of premenopausal women and vegetarians, since iron is harder to absorb from plant than animal sources. Too much iron may be dangerous, as it can elevate cholesterol, so don't take iron supplements without seeing your doctor and getting tested.

Instead of overhyped supplements: To maintain vital levels, eat a balanced diet supplemented with an ordinary multivitamin that has 100 per cent of the recommended dietary intake for B vitamins and iron. Nothing fancy required: the Centrum Multivitamin and Mineral Supplement contains the right mix and amounts of these two nutrients.

MYTH: Herb-fortified drinks give you a boost

Ingredient lists on drinks can sound like species of lizards (ginkgo biloba, taurine, guarana), "For most of these ingredients, there's no research to back up the claims," Diekman says. "That doesn't mean you can say conclusively that they don't work, but there just aren't enough high-quality studies to substantiate the claims." (Without studies, there's also insufficient evidence for safety.)

In reality, the boost you're getting from these beverages is the same from a Diet Coke: caffeine. It works as an energy-booster by jamming up adenosine - a chemical that slows down nerve activity in your brain. The adenosine receptors bind to the caffeine instead, which means you accelerate instead of slowing down.

Instead of energy drinks: To keep your caffeine levels optimal through the day and your sugar in check, swig drinks at strategic times - when you arrive at work in the morning and when you hit the midday slump. Researcher Dr James Wyatt suggests aiming for 25 to 50mg per serving. (See Buzzworthy for how much caffeine popular drinks deliver.) Dr Wyatt warns that caffeine sensitivity varies - you'll know whether that's too much or not enough. If you have a two-lattes-in-the-morning habit, though, it won't work so well; regular use can decrease sensitivity.

As a bonus, coffee-drinking has been linked with a decreased risk of Parkinson's disease and type 2 diabetes, and the antioxidants called flavonoids in tea may help fight heart disease and even some cancers. Unless spiked with sugar, cream or syrup, both coffee and tea fight fatigue without a kilojoule cost - that means free energy for you.

Buzzworthy: find out the caffeine levels in some popular drinks.