5 reasons you can't concentrate

You walk into a restaurant to meet a friend and remember you were supposed to meet somewhere else. You leave your boss's office and, quick as that, forget the deadline she gave you for a new project. You had your keys in your hand, you were just holding them, and now they're gone — again.

What's going on? Here, nine possibilities for why your mind is wandering, and expert advice on how to get your concentration back.

1. Your numbers are low
Fuzzy mindedness could signal a vitamin or hormone deficiency, especially if you're also feeling unusually tired. For example, hypothyroidism—too-low levels of thyroid hormone—could be to blame, says Dr. Robert Orford, consultant at the Mayo Clinic's Preventive Medicine Division in Scottsdale, Ariz. "If there's a deficiency in thyroid hormone, metabolism slows, which reduces blood flow and cellular function in various parts of the brain."

B-12 deficiency and related anemia can have similar symptoms. Most people get plenty of B-12 in their diet, but an underlying condition such as Crohn’s or celiac disease can prevent your body from absorbing it.

Try this: Schedule an appointment for a physical with a doctor who'll take time with you. Make a list of any other health changes you've noticed that could help pinpoint the source of your problems concentrating.

"You want a comprehensive medical exam, including blood tests," says Orford. Also ask your doctor to test for cardiovascular risk factors such as hypertension, high cholesterol, metabolic syndrome or prediabetes: If left untreated, they can cause cognitive decline.

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2. Your hormones have gone haywire
If you're nearing the end of your baby-making years, your inability to think clearly may signal the start of perimenopause — that run-up to menopause when menstrual cycles become irregular and estrogen drops. Lack of concentration is a common complaint of perimenopausal women, says Dr. Kimberly Pearson, a psychiatrist at Massachusetts General Hospital's Center for Women's Mental Health. "They describe it as feeling fuzzy. That's the word a lot of women use. They feel like their vocabulary is diminishing, like they're not as sharp, not as crystal clear."

Try this: If other signs point to perimenopause (hot flashes, night sweats, vaginal dryness), consider short-term hormone replacement therapy to get you over the hump.

"Women who go on replacement notice such a shift," says Pearson. "They say, 'Oh my God, I have my brain back.'" If HRT is out because of the health risks involved, ask your doctor about the possibility of taking a low-dose, concentration-boosting stimulant such as Ritalin instead. "And exercise seems to help everything," says Pearson.

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3. You've changed your meds
Anti-depressants can affect mood and concentration when you go on or off them. Antihistamines, sedatives, and anti-anxiety medications can cause lingering drowsiness, and antidepressants, beta blockers, and other medicines can cloud your mind. People who take statins sometimes notice a loss of mental clarity, says Orford.

A daily dose of Coenzyme Q10 may counteract this effect. As for sleeping pills — please.

Try this: Write down all the meds you take or recently stopped taking and review this list with your doctor. Ask if any of them are known to cause concentration problems when people go on or off them, or mix them with other medications, or take them long term. Educate yourself about the drugs on your list so you can have a more fruitful discussion. Go to the National Library of Medicine's PubMed Health, MedLine Plus and DailyMed Web sites for good information.

4. You're quitting smoking
Yaaay! Two things to remember when you're tempted to cheat: 1. The more and longer you smoke, the more gray matter you lose. That's proven. The sooner you quit, the more you maintain. 2. Yes, you'll have trouble concentrating as you go through nicotine withdrawal, says Christopher Kahler, professor of behavioral and social sciences in the public health program at Brown University. It's a common complaint. But that passes, and the mental-health boost you get from quitting more than compensates: You did what? You quit smoking? Wow.

"There's a lot of psychological benefit to it," he says.

Try this: The happier you feel when you tackle quitting, the more likely you are to succeed, says Kahler. His tips for boosting mood: Track three good things that happen to you each day and write about them each night. Write a letter of thanks to someone you never thanked for something and deliver it. If you can spend some of the money you save by not smoking, skip the material purchases and do something fun with a friend. Shared experiences generate lasting happiness.

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5. Your diet has deteriorated
What you eat can have a major impact on mental clarity, says Laura Middleton, assistant professor of kinesiology at the University of Waterloo in Ontario. Bad eating habits increase your risks of obesity, hypertension, high cholesterol and related ills that can impair cognitive function, and being overweight or obese makes it harder to stay active, which is essential for brain health.

Try this: Middleton's motto is "If it's good for the heart and cardiovascular system, it's good for the brain." She advises sticking to the principles of the Mediterranean Diet: A diet high in fish and vegetables and lower in meat, saturated fat and processed foods. If sweets and other junk food are your downfall and you're able to cut back, magic can happen: Brain fog, energy crashes, hunger pangs may dissipate.

Click here for more reasons why you can't concentrate from Prevention.