There Are Healthy Ways to Help You Work Harder for Longer There is no substitute for adequate sleep but some supplements and lifestyle changes give you more useful energy when you wake up.

We all have the limitation of 24 hours in a day. No matter what you do, that's all the time you have. It's a great equalizer among entrepreneurs.

Getting ahead means doing more within the 24 hours that you have. That's one reason why off-label Adderall use has increased 67 percent in the past six years, and high performance individuals from Silicon Valley to Wall Street are using smart drugs like modafinil. Where would any small business be without the ubiquitous pot of coffee?

The biggest problem with this approach, which nearly all entrepreneurs find out the hard way, is that it is not sustainable for long. If it was possible to just continue drinking more cups of coffee, the thriving nootropics industry wouldn't be growing. People realize that stimulants don't last forever, and they want an alternative.

Related: 5 Mind Hacks Silicon Valley Founders Use to Stay Focused

Luckily, the solution comes from high school biology.

Increased energy and the mighty mitochondria.

Entrepreneurs confuse mental stimulation with mental energy. The chemical form of energy is ATP (adenosine triphosphate), which is produced in each of our cells by the mitochondria. Remember the "powerhouse of the cell" and "mighty mitochondria" conversations in biology class?

By increasing the health of our cells and producing more ATP (energy), we can actually do more work for a longer period of time. With more energy, our brain and body has more endurance which allows us to tackle the hard problems for many more hours during any given day.

In contrast to this, stimulants usually increase productivity in the short-term, but reduce the ability to work for long periods. There is a reason so many people complain about a "crash" associated with drinking coffee. We trade off greater focus and concentration in the short-term for less mental energy only a few hours later.

Most people would benefit from focusing on increasing real energy.

Related: Supplements and Health Tips That Will Improve Your Mindset

How to combat fatigue to work longer.

Creatine is a perfect tool for increasing ATP. Even though it has a reputation for meatheads and gym jocks, creatine works in a similar way for the brain as it does for the body. One study found that creatine could reduce fatigue by up to 90 percent.

Another study showed that after only five days of taking creatine, subjects doing math calculations became fatigued far slower. The subjects were able to do more work -- math calculations -- for a longer period.

Besides the immediate benefits of creatine, there are numerous advantages like neuroprotection and neurogenesis (growing new neurons) all because the cells have more energy to function.

Here are other supplements useful for increasing energy and reducing fatigue as well:

• Coenzyme Q10 (CoQ10) -- We have coenzyme q10 in our cells at all times, but sometimes more can aid in our mitochondrial health. The effects of added energy from CoQ10 have been shown to translate into antidepressive effects and neuroprotection.
• Glutathione -- According to Dr. Mark Hyman, glutathione is the "mother of all antioxidants." This helps to remove free radicals and pollutants out of the air, but most importantly it can increase the health and energy production of our mitochondria.
• Nicotinamide riboside -- This byproduct of cow's milk and brewer's yeast can have tremendous energy boosting benefits. By increasing the health of our cells, as with the other nootropics, this option can reduce our fatigue and allow us to work longer.

If supplements aren't your style, there are a few lifestyle habits you can take advantage of as well. Fasting is a practice many Silicon Valley executives are using to increase their mental energy and endurance. If skipping a meal sounds too daunting, spend 15 to 20 minutes in a sauna, and you can experience similar results.

Related: 11 Tips to Stay Productive When You're Tired

Whichever methods you choose, improving real energy will be the ticket to mental endurance and creating better work. You may not have the subjective feeling of stimulation that comes with caffeine or modafinil, but the effects are noticeable and sustainable.