TL;DR: Dehydration causes a number of changes that cause, including swelling of the blood vessels in your brain, changes in blood pressure, and stress on your blood vessels. Being thirsty on main is bad for your heart.

Metabolic tips for reducing headaches and stress to blood vessels:

• Drink enough water. If this is something you forget to do when the day gets busy, set a timer for 1 hour and drink a glass of water when it goes off. You should have to pee once every 1-2 hrs throughout the day.

• Move around for a few minutes every hour - this will help the exchange of fluids between your gut, blood, and lymph and help the water you drink actually hydrate your body.

• Avoid drinks with caffeine or sports drinks unless you’re actively sweating.

Proper hydration is an important part of your “nutrition” plan. Dehydration decreases blood volume and slows down how quickly nutrients, including glucose, can get to your different organs.

You are alive because of a well-coordinated dance between nutrients in your body. You remember hearing somewhere along the way that “the mitochondria is the powerhouse of the cell”? (I know what you’re thinking: is this professor about to get deep on the mitochondria? Okay, Sarah, talk nerdy to me.) For now, you just have to remember that the mitochondria makes most of the molecule that carries “energy” around your body (ATP).

Energy is actually made when mitochondria burn molecules as fuel. How does fuel actually get to the mitochondria? It has to get into the cell - the mitochondria can break down molecules (the technical term is “oxidize” because it uses oxygen HOW CREATIVE) that got imported in from the blood. Molecules imported in from the blood can either be used immediately - like when you’re running/cycling/exercising after fasting & your muscles pulling glucose out of the bloodstream to keep you moving. Or they can be stored for use later - like when insulin tells your fat and liver cells to pull glucose out to bring down BGLs when you’re not moving. (Glucose is not the only molecule your mitochondria burn, obvs; we’ll get to some of the other molecules that get oxidized later).

Side note: insulin will tell your muscles and liver to get glucose out of the blood, but it doesn’t have to be stored as fat. Glucose can be stored as glycogen IF your glycogen stores are low. How do you lower your glycogen stores? Guess. Or ask. Or read more later.

So how do molecules that will be burned as fuel get into the cell? Fuel travels through your blood. If your blood is not moving well, your cells aren’t getting the fuel they need to keep you, well, fueled. Does low blood volume, or low fuel levels, contribute to feeling tired? Yes. Lower blood volume also sends a signal to your brain that your blood glucose levels (BGLs) are about to go all out of whack since your body is concerned about the concentration of glucose. The same total number of glucose in a smaller volume = more concentrated. And any changes to the total number of glucose molecules in a smaller volume are going to have a much larger effect on the concentration, which throws your body into a cycle of over-compensating and fishtailing back and forth to try to adjust and maintain proper BGLs.

Dehydration causes lower blood volume = changes in blood pressure that cause headaches. In an effort to make up for the lower blood volume, your brain will release a hormone called vasopressin to try to retain water in your body so you don’t lose more blood volume. Vasopressin also tells your liver to release more glucose into the bloodstream. This is an attempt to counteract the reduced speed of glucose delivery by simply flooding the system - if it’s going to take longer for the glucose to show up, at least there can be more of it when it gets there. This is a short-term solution at best, since the increased BGLs are also stressful to the cells that make up your blood vessels (aka vascular epithelial cells).

Chronic dehydration leads to sustained high BGLs, which interferes with proper blood vessel function. In addition to changes in blood pressure from the hormones your brain releases, blood vessels themselves contribute to your blood pressure. Blood vessels need to be elastic - they expand when the heart pumps blood and they constrict after that rush comes through to help keep pushing the blood around your body. If your heart had to generate all of the force needed to move your blood around, it would break (and sometimes it does if your blood vessels lose elasticity…) Moving our blood around, either by exercise, certain yoga poses, or massage, does a lot to help our heart out.

Changes in the size of our blood vessels is called dilation and sustained high BGLs, or other factors that induce insulin resistance, interfere with the blood vessels’ ability to dilate properly.* This leads to all sorts of problems, including higher risk of cardiovascular disease and atherosclerosis, but the one you feel on a daily basis is headaches and general fatigue.

Seriously, don’t be caught out there acting thirsty.

Metabolic tips for reducing headaches and stress to blood vessels:

• Drink enough water. If this is something you forget to do when the day gets busy, set a timer for 1 hour and drink a glass of water when it goes off. You should have to pee once every 1-2 hrs throughout the day.

• Move around for a few minutes every hour - this will help the exchange of fluids between your gut, blood, and lymph and help the water you drink actually hydrate your body.

• Avoid drinks with caffeine or sports drinks unless you’re actively sweating.

*It’s been known for a while that nitric oxide (NO) is an important vasodilator. Recent work is also shedding light on how insulin resistance in vascular endothelial cells interferes with NO production.

Chen et al., (2008) Nitric Oxide in the vasculature: where does it come from and where does it go? A quantitative perspective. Antioxid-Redox Signal.

Park et al., (2022) Endothelial cells induced progenitors into brown fat to reduce atherosclerosis. Circulation Research.