What Is the Main Idea?

The exact causes of migraine are unknown, but it is thought that migraine attacks develop as a result of abnormal brain activity. In the research article “Migraine Attacks Triggered by Ingestion of Watermelon”, published in the journal European Neurology, the authors describe how watermelon consumption may trigger migraine headache attacks by activating a process called the L-arginine-nitric oxide pathway.

 What Else Can You Learn?

In this blog post, different types of migraine and what is known about how migraine attacks develop are described. The processes by which nerves transmit signals throughout the body and the L-arginine-nitric oxide pathway are also discussed.

What Is Migraine?

Migraine is often characterized as a headache that causes severe throbbing pain or a pulsing sensation, usually on one side of the head. However, there are different types of migraine and headache, and it can be difficult to tell them apart. Different people also experience different migraine symptoms.

Although many migraine attacks involve a severe throbbing headache, some people will experience migraine attacks without headache (known as silent migraine). When this happens, the person experiences “aura” symptoms such as flashing lights or seeing zigzag lines, but does not develop head pain.

Other people may experience migraine that includes severe head pain with or without aura symptoms, such as changes in their vision, numbness or tingling, feeling dizzy, having difficulty speaking, and feeling or being sick. Migraine attacks can last anywhere between several hours and three days, and symptoms may start and end one or two days before headache develops.

What Causes Migraine?

The exact causes of migraine are not known, although the fact that people are more likely to get them if they have a close family member that gets migraines suggests that there is some sort of genetic involvement. It is thought that migraines develop when nerve signals, chemicals and blood vessels in the brain are affected by abnormal brain activity.

Neurogenic inflammation (a type of inflammation caused when particular types of nerves are activated and release mediators of inflammation such as nitric oxide) and the widening of blood vessels in the membrane layers that protect the brain and spinal cord are believed by some researchers to be key causes of migraine headache. Leakage of blood plasma (the liquid component of blood that does not include blood cells) from blood vessels into the surrounding tissues may also be involved.

Nerves (also known as neurons), together with the spinal cord and brain, are key components of the nervous system and consist of bundles of nerve fibers wrapped up to form cable-like cells. Nerves send electrical signals that control our senses, like pain and touch, and essential processes such as breathing, digestion, and movement, from one part of the body to another. When an electrical signal reaches the end of a nerve it is converted into a chemical signal. This causes molecules called neurotransmitters, such as dopamine and epinephrine (also known as adrenaline), to be released into the space between the end of one nerve and the start of the next one, which is called a synapse.

Once they have crossed the synapse, the neurotransmitters bind to receptors on the new nerve, and the signal is converted back into a chemical signal and travels on along the neuron. The ability of nerves to transmit signals internally or between one nerve and another is dependent on a process called depolarization, which is essential to the function of many cells and communication between them. Most cells have an internal environment that is normally negatively charged compared with the cell’s external environment.

When depolarization occurs, the internal charge of the cell temporarily becomes more positive before returning back to normal. Migraine aura is thought to be caused by a wave of “spreading depolarization” in a part of the brain called the cortex. Nitric oxide and glutamate are released during spreading depolarization, and some studies have reported increased levels of nitric oxide during headache attacks. This has led some researchers to suggest that the pathways that break down nitric oxide may be involved in migraines.

What Did This Study Investigate?

Although the exact causes of migraine are still unclear, migraine attacks are known to be triggered by stress and tiredness, hormonal changes, prolonged fasting or skipping meals, and the consumption of too much alcohol or caffeine and certain foods. Watermelon is the main natural source of an amino acid (the component units that are joined together to make proteins) called L-citrulline (in fact, its name is derived from the scientific name for watermelon, Citrullus vulgaris).

L-citrulline is also made by the body in the liver and intestine, and is an important component of the urea cycle, the process by which toxic ammonia is converted into urea so that it can be passed out of the body in urine. L-citrulline in the body can be converted to another amino acid called L-arginine, from which nitric oxide is produced via a process called the L-arginine-nitric oxide pathway. This means that watermelon may be an indirect source of nitric oxide in the body and may trigger migraine in some people.

The authors of this study conducted a clinical trial to investigate whether eating watermelon causes headache attacks in people who experience migraine. They recruited 38 volunteers who experience migraine without aura and 38 who do not, and asked them to each consume a portion of watermelon after avoiding consumption of watermelon and other L-citrulline-containing foods in the preceding 7 days, and fasting for the preceding 8 hours.

All of the volunteers gave blood samples before and after eating the watermelon to enable the researchers to assess whether there were any changes in blood serum nitrite levels (produce by the breakdown of L-citrulline). All of the volunteers then ate and were followed up for 24 hours by telephone, so that the researchers could be informed if any of the volunteers developed headache.

What Were the Results of the Study?

Headache was triggered in almost one-quarter of the people in the group who experienced migraine (23.7%) after, on average, around 2 hours after watermelon was consumed. In contrast, none of the volunteers in the migraine-free group developed headache over the 24-hour follow-up period. Interestingly, around one-quarter of the volunteers in the migraine (23.4%) and migraine-free (24.3%) groups were shown to have increased nitrite levels in their blood serum samples after consuming watermelon. These increases from the values recorded before watermelon consumption were statistically significant.

These findings suggest that eating watermelon can trigger headache attacks in people who experience migraine and increase serum nitrite levels, which may be due to activation of the L-arginine-nitric oxide pathway. Although everyone is different and not all of the migraine group volunteers developed headache after consuming watermelon, people who experience migraine may wish to consider reducing or avoiding consumption of watermelon.

Note: This post is based on an article that is not open-access; i.e., only the abstract is freely available.

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