Although they are not the only organs affected by lack of water, the brain and eyes are especially vulnerable during dehydration.

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Busy lifestyles and processed foods and beverages cause nearly all of us to become chronically deprived of water and susceptible to the dangers of dehydration._[1] Although they are not the only organs affected by lack of water, the brain and eyes are especially vulnerable to the following conditions:

• Obstruction of blood supply to the eyes
• Swelling of the eyes
• Impaired vision
• Shrinking of the cornea
• Decreased brain volume
• Increased energy consumption in the brain
• Impaired mental function and fatigue.

When deprived of water, cells shrink and fail to transport nutrients, use energy, grow, divide, replicate DNA, or communicate with each other. Fortunately, drinking filtered and non-fluoridated water can prevent and reverse these problems that are commonly treated with medication and surgery.

Eyes Suffer from Lack of Water

Dehydration can cause occlusion of the central retinal veins, which carry blood out of the eyes._[2-4] As a result, the eyes cannot receive adequate blood flow and the buildup of blood that cannot leave the eyes causes them to swell._[4,5] This causes retinal swelling and can reduce vision from a perfect 20/20 to a visually impaired 20/70._[4,6].

Furthermore, blood clots can develop in the central retinal veins due to chronic dehydration. Dehydration also causes thinning of the cornea, the part of the eye that enables it to focus light._[7] This could explain the mysterious condition of keratoconus, in which the eye protrudes into a cone shape and requires surgery in order to correct. It is believed that when the cornea becomes too thin, it fails to withstand the pressure of the fluids inside the eye._[8] It then protrudes and causes blurriness and double vision.

Dehydration Shrinks the Brain

Studies using MRI scans have demonstrated that the brain shrinks when it becomes dehydrated._[9,10]

Like most cells, neurons consist of more than 70 percent water. When water content diminishes, axons and dendrites shrivel and become smaller in diameter, making it more difficult for signals to pass through them. As a result, the brain needs to consume more energy to move signals between cells, which leads to constant tiredness and mental fatigue._[11]

Specifically, this condition causes the following:

• Inability to plan
• Bad mood
• Lower concentration
• Headaches
• Increased difficulty in performing tasks._[12]

Both white and gray matter is known to shrink in more than four different regions of the brain, which is considered to be a contributing factor to cognitive impairment and even Alzheimer’s disease._[13,14]

Solutions to Brain and Eye Dehydration

Adequate water intake can reverse all of these problems. Studies indicate that rehydration eliminates pain signals in the brain and restores its normal activity levels._[15] Mental fatigue and tiredness are reduced when the brain is no longer required to spend larger amounts of energy to transmit signals.

Brain size is also shown to be restored when adequate water supplies become available._[10] The thickness of the cornea can also be restored with water, but if blood clots in the central retinal veins have developed, proper hydration may not be sufficient for repair. Coconut water is another very effective hydration booster.

Important Tip on Hydration

It’s important not to trade the dangers of dehydration for the dangers of unfiltered water. For adequate hydration, men should drink three liters of water per day and women should drink 2.2 liters per day._[17]

But tap water is not the answer. Tap water contains more than 792 chemical contaminants, including the dangerous neurotoxin fluoride._[16] Check here for reasons why you should never drink unfiltered water, and check here to find out which type of water filter is best for your needs. Every cell in the body is negatively affected by dehydration, making it a problem that should be fixed even before symptoms become obvious.

After the body is rehydrated, drinking more than these quantities is unnecessary. Remember that soft drinks and other types of flavored beverages are not adequate sources of water and that some may actually have dehydrating effects.

For related reading, visit these posts:

• Dehydration Headache: Know the Causes, Signs, and Treatments
• Do You Have Chronic Dehydration?
• Natural Cures for Nausea and Dehydration
• Watch for Signs of Dehydration in Children: Most Kids Don’t Drink Enough Water

[1] Nutr Health Aging. 1997;1(3):151-5.
[2] Acta Ophthalmol Scand. 2003 Aug;81(4):415-6.
[3] Metab Pediatr Syst Ophthalmol. 1988;11(1-2):67-9.
[4] Ophthalmic Surg Lasers Imaging Retina. 2014 Apr 9;45(3):e23-5.
[5] Retina. Mar 2010; 30(3): 479–484.
[6] American Optometric Association.
[7] Cornea. 2006 Feb;25(2):182-4.
[8] Funct Biomater. Nov 13, 2012; 3(4): 760–775.
[9] Int J Sports Med. 2005 Jul-Aug;26(6):481-5.
[10] Neurology. 2005 Feb 8;64(3):548-50.
[11] Hum Brain Mapp. 2011 Jan;32(1):71-9.
[12] Nutr. 2012 Feb;142(2):382-8.
[13] PLoS One. 2012;7(8):e44195.
[14] Nutr Health Aging. 2010 Dec;14(10):823-7.
[15] Anesth Analg. 2013 Dec 31.
[16] Environmental Working Group.
[17] Ned Tijdschr Geneeskd. 2010;154:A1757.

Originally published in 2016, this post is regularly updated.