Nutrition is of paramount importance to your energy levels and alertness, and it's so multifaceted that it can be next to impossible to cover all your bases and make sure you're consuming everything you need. Blood tests can tell you where you're deficient, but trial and error also works.

Vitamin D is something we all need but most of us don't get enough of. When I say most Americans are deficient in vitamin D, I'm talking roughly 75 percent of us. Studies have found that getting adequate vitamin D significantly improves fatigue. We get so little from natural sources like the sun, that supplementing becomes almost mandatory.

Iron deficiency is another cause of tiredness, and it's one of the most (if not the most) common deficiencies in the world.

There are a number of nutrient deficiencies that cause fatigue, including magnesium, potassium, folic acid, and vitamin B12 deficiencies. Evaluate your nutrition to find any gaps.

You already know that sitting is bad for you, so I'll spare you those details; but do you know that specifically, sitting is making you more tired? Studies have found a correspondence between uninterrupted and prolonged sitting, and fatigue. When participants were required to get up and walk periodically, the light activity was observed to be an effective countermeasure to their tiredness. Even just a little bit of movement helps increase blood flood, carrying more oxygen and nutrients throughout your body. The result is more energy and alertness, and improved cognition. Also, it helps you sleep better — which helps you feel less tired the next day. It's a neverending cycling!

Really, it's science 101 (or Newton's first law of motion): In a nutshell, an object at rest stays at rest. An object in motion stays in motion. Want to feel less drowsy? Get up and do a little dance.

The fact that you need to drink a lot of water to stay healthy and hydrated isn't exactly breaking news; but 75 percent of Americans are still walking around dehydrated every single day. Most often, we only realize we're dehydrated once we're thirsty; in reality, it can start long before this.

Perhaps unsurprisingly, dehydration is a common cause of fatigue. According to the Natural Hydration Council, 10 percent of cases of tiredness are caused by dehydration. Research says that millions of people are visiting their general practitioner every year with symptoms like tiredness, commonly caused by dehydration.

Make no mistake about it: A lot of us aren't drinking enough water; and it can take just three percent loss of body weight due to hydration to make you tired.

Our bodies have this internal clock that wants consistency. It doesn't like it when we sleep in some mornings and wake up super early others, or stay up late one night and hit the hay early the following. By having an inconsistent sleep schedule, you're essentially putting your body through jet lag, minus the travel. It confuses our bodies so much that even if you sleep long enough, you still won't feel rested if you woke up at an unusual time. It's almost like having a hangover, except you didn't get to get drunk first (and where's the fun in that?).

The standard American diet is nothing to brag about; and yet shockingly, many of us undereat. This is likely due to a culture that, for years, has claimed that fewer calories equal a slimmer figure, plain and simple. (In reality, it is not that simple — not even close; but that's another conversation.) Maybe you're limiting calories because you're trying to slim down (remember — you're beautiful no matter what); maybe you have such a hectic schedule that you sometimes just forget to eat. It happens! But know this: That constant drowsiness you're always battling? That could be due to a deficit of calories.

Our bodies function largely thanks to glucose — carbohydrates. Carbs have long been considered the enemy; but nothing could be further from the truth. If you've gone too long without eating, your body is depleted of glucose, and you feel tired. You may also notice you have difficulty concentrating. Your brain uses twice as much energy as some of the other cells in your body. What do you think happens when your brain and body don't have the glucose they need to operate properly? They slow down. They lag.

Seriously, people. Don't be afraid to eat. This is how we fuel our bodies.

So, we know that an unpredictable schedule is no good for your energy levels. There's something else to consider, though. It's not uncommon that we sleep very little throughout the week, all because we know we'll "catch up" on the weekends. Not only does this totally break the find-a-consistent-sleep-schedule rule, but repetitive under-sleeping is all kinds of bad news.

I'm not just saying that skimping on sleep makes you tired — no kidding. I'm saying that repeated skimping can lead to semi-temporary exhaustion — something that can't be cured with a few extra hours of rest. Don't be fooled by your late weekend mornings, when you don't set an alarm: There is no such thing as "catching up" on your sleep. "Sleep debt" is the phrase experts use to describe the lack of sleep you've built up, even when you attempt to catch up. They estimate that on average, Americans are losing about two full weeks of sleep each year.

The cure? It's not a quick fix, but rather a lifestyle change. Focus on adding an hour or two of sleep to your schedule every single day. Gradually, you'll pay off your "debt."

The messy one and the neat freak: We are forever debating the pros and cons of both. But science has found that there is indeed at least one drawback to being surrounded by too much clutter: It competes for your attention. Whether it's physical and literal or emotional, having too much "stuff" happening around you negatively impacts your ability to focus and process information. The result is decreased performance, stress, and feelings of being overwhelmed or even suffocated. Clutter attacks our mind with too much stimuli, forcing us to work even harder to focus on things — even things that aren't that important. No wonder clutter can exhaust us!

Your home and work area don't need to be completely spotless, but try clearing out some of your excess "stuff" — whether that's clothes you don't wear, paperwork that should be filed, or unread emails — and you might just notice you feel more energetic, productive, efficient, and awake.