En‘lightning’ the impact of atmospheric conditions in headache

The weather has long been known to affect well-being and provoke the emergence of various symptoms in humans. Headache was reported to be one of the most frequent symptoms associated with altered weather conditions (1). Migraineurs also claim atmospheric weather as a potential trigger for migraine (2), though many studies either failed to show a link between particular weather components and incidence of headache or produced conflicting results in investigating major atmospheric variables such as atmospheric pressure, temperature, humidity, wind or thunderstorm activity (3–7). One of the problems was the difficulty of evaluating a single atmospheric variable alone since weather change is usually accompanied by the alteration of more than one atmospheric factor. For instance, reduced atmospheric pressure, a relatively lower pressure zone than that of the surrounding area, drives movement of air and is generally associated with increased temperature, winds, and humidity, facilitating the development of clouds, precipitation, and thunderstorms (8).

In the accompanying article, Martin and colleagues conducted a study to investigate whether lightning days were a risk for headache (9). Lightning is an outstanding atmospheric event and several previous studies have failed to provide its correlation with the incidence of headache/migraine (6,7). Instead of using visible lightning or audible thunder to define lightning, Martin and colleagues obtained data from ground sensors detecting electromagnetic radiation from cloud-to-ground strikes in their study (9). By providing a more accurate depiction of the frequency and current of lightning strikes, researchers indicated that there was a relationship between lightning and headache. It was an observational cohort study using headache data obtained from past clinical trials that were conducted in a population of mainly female migraineurs in the Midwest region of the United States. They reported that lightning and associated meteorological changes were notable trigger factors for headache. Compared to non-lightning days, lightning days were associated with a 31% increase in the frequency of headache and a 28% increase in the frequency of migraine. Furthermore, the authors found 23% new-onset migraine attacks on lightning days. Thereby, they concluded that lightning seemed to be associated with the presence of headache in migraine patients.

What exactly happens during lightning? During a storm, colliding particles of rain, ice crystals, or snow and their strong movements increase the electrical imbalance and negative charge of the lowermost part of storm clouds. The electrical discharge occurs as a result of imbalance between negatively charged storm clouds and positively charged objects on the ground. When a climbing surge of positive electricity called a streamer makes contact with a channel sent from a cloud, an electric current wave propagates up the channel as a bright pulse and generates lightning (10). Lightning produces enormous power and heat, and each strike can contain several hundred million volts of electricity. Lightning heats the surrounding air up 30,000 degrees Celsius, and fast expansion of heated air generates audible pressure waves (10). Such an energy outbreak induces rapid change in the chemical composition of the atmosphere. Nitrogen oxides (NOx = NO + NO₂), primarily NO with considerably less NO₂, are produced in high-temperature lightning channels (10). NO, a precursor to ozone (O₃), plays an important role in regulating the concentrations of O₃ and OH in the atmosphere. Lightning is very frequent during certain seasons and significantly contributes to the global NOx burden.

Consistent with the above notion, dust is one of the important components of complex atmospheric weather. Dust originating from large deserts travels all around the globe and has an adverse effect on public health (11). African dust, a major source of global dust, has been shown to contain bacteria, viruses, fungi, spores, iron, ions, amino acids, and other molecules (11,12). Therefore, it is also easy to associate migraine or asthma attacks with dust. Increased acute asthma visits that show comorbidity with migraine are reported to be associated with increased Saharan dust cover (13). Recently, an experimental study demonstrated that African dust-laden air activated trigeminal nucleus caudalis and that a nociceptive effect was not mediated by dust itself or attached living microorganisms, but rather by other molecules or byproducts smaller than 450 nm (12). Inhalation of African dust-laden air also induces a plasma NOx increase in rodents with trigeminal nucleus caudalis activation (12). It is also notable that microorganisms attached to African dust are viable for centuries, as a recent publication revealed that microorganisms from a dust sample obtained by Charles Darwin 150 years ago were alive and multiplied (14). Dust-laden weather is usually accompanied by low atmospheric pressure, warm air, wind, precipitation, and thunder. Furthermore, certain weeks, months or seasons are more prone to carry dust and other particles including iron;precipitation and humidity are important in the neo-formation of iron nanoparticles (15). When dust presents in the atmosphere the likelihood of lightning is increased and the threshold to generate lightning is possibly lowered by its composition of iron, water, ice, and other particles that facilitate the passage of electrical current. Pähtz et al. have shown that grains in desert storms spontaneously generate strong electrical charges though even the simplest aspects of its causes remain elusive because it is difficult to understand how inert grains in contact with little more than other inert grains can generate the large charges observed (16). Saydam and Senyuva (17), however, demonstrated that on contact with cloud water, dust matrix undergoes rapid alterations and changes the ionic composition of clouds that enables strong electrical discharges. Thus the presence of dust increases the probability of cloud-to-ground lightning flashes. In confirmation with the latter view, Jenkins and Pratt reported that tropical storms developed in the eastern Atlantic were associated with dust outbreaks, elevated ice contents, and frequent lightning (18). In turn, an increased chance of lightning in dust-laden atmosphere would yield favorably higher bioreactive molecules such as NOx, ozone, iron to the atmosphere in the presence of a very rich environment provided by desert dust.

The molecules and mechanisms generating headache during lightning and accompanying atmospheric conditions remain unclear. However, it is highly probable that inhalation is the major route for airborne atmospheric factors to trigger headache. NO and its pivotal role in migraine pathogenesis are well known (19). NO donors are commonly employed to induce headache in clinical studies, and preclinical experiments have also delineated NO-induced cellular mechanisms (20,21). Since lightning channels are significant sources of atmospheric NOx, it may be expected that an inflammatory cascade involving inducible nitric oxide synthase (iNOS) and nuclear factor kB (NFkB) would operate in biological systems having head pain on days of atmospheric conditions producing lightning. A lightning channel with all its branches also radiates electromagnetic impulses called sferics that can propagate thousands of kilometers from their source and give direct information about thunderstorm activity on the ground. Sferics are very low and low-frequency electromagnetic waves between 1 Hz and 30 KHz, which were associated with migraine headache (7) and,with blood-brain barrier disruption in a preclinical study (22), may indicate another mechanism for headache. Foley and colleagues (23) reported a novel route that electromagnetism could be transducted in the retina and sensed through the vision system in humans. This is a fascinating finding given the fact that the visual system plays an important part in migraine pathogenesis and symptoms. In addition to sferics, charged ions, yielded during thunderstorms, were also implicated in headache attacks. Martin et al. also noted that, if the lightning strikes occurred with a greater negative polarity, the risk of headache was further increased (9). Greater negative polarity of lightning could indicate the presence of positive air ions that was shown to be associated with migraine attacks (24).

The results of the study have to be reconsidered because of limitations. Individual risk factors or seasonal sensibility could not be excluded, since each patient was not followed for an entire year. The majority of patients were women, and other trigger factors along with weather were not evaluated. In fact, migraineurs report multiple triggers and attacks usually occurring in conjunction with other triggers. Furthermore, the study was not corrected for multiple comparisons since lightning and weather variables are highly intercorrelated. Additionally, data were not obtained from the same time period in the study group. Spring is the most critical time of the year in the northern hemisphere where composite weather (low pressure, warm air, wind, rain, storms, lightning) are mostly encountered, desert dust outbreaks, and accompanying bioavailable iron and other molecules reactive in biological systems are plentiful. Lightning is also common during the spring, which contributes significantly to the NOx load. Clinical study also suggests that spring is the time of the year that migraine frequency is increased (25). As a last point, all patients, assumed to be within the 30 miles of the nearest post office, may not be equally affected by lightning and its consequent bioactive by products.

In brief, one can only conclude that weather conditions associated with lightning have the potential to induce headache in migraine patients. Other determinants in the atmospheric environment enabling lightning or the consequences of lightning play a principal role in triggering headache. In support of that view, Vaitl and colleagues reported that migraine headache was correlated with sferics but not with thunderstorm activity (7). A detailed prospective clinical study that explores every single item including dust, microorganism, and bacterial and fungal spores, charged ions, sferics, NOx, nanoparticles, bioavailable iron content in the weather besides other well-known parameters such as pressure, temperature, humidity, rain, and lightning is required to begin to solve that puzzle.