Dietary Sodium Intake and Migraine: Is Salt the Answer?

In the study entitled “Severe Headache or Migraine History Is Inversely Correlated With Dietary Sodium Intake: NHANES 1999-2004,” Pogoda et al found an inverse relationship between migraine and dietary sodium intake. The authors conclude that future studies are necessary to determine whether altered sodium homeostasis is causal in, or an effect of, migraine. The study results are not surprising considering an intricate relationship between migraine and the autonomic nervous system, which plays a major role in the pathophysiology of migraine. Besides the cranial autonomic symptoms that may accompany migraine and other primary headache disorders, patients with migraine have significant abnormalities on the autonomic function tests with evidence of sympathetic overactivity and decreased parasympathetic activity. Patients with migraine also have a higher prevalence of the autonomic symptoms, such as dizziness, vertigo, syncope, and orthostatic intolerance. Conversely, headache, including migraine, is the most common comorbidity in patients with autonomic disorders, such as postural tachycardia syndrome (POTS) and neurocardiogenic syncope, with the prevalence ranging between 27% and 96% in some case series. One of the major underlying mechanisms in autonomic disorders, such as POTS, neurocardiogenic syncope, and orthostatic hypotension, is hypovolemia, which may be due, in part, to the disturbance of the renin-angiotensin-aldosterone system and resultant abnormalities in sodium and water retention. The first-line therapeutic intervention for patients with autonomic disorders is plasma volume expansion via increased water and sodium consumption, which are effective nonpharmacologic measures for raising blood pressure, reducing orthostatic blood pressure drop, and ameliorating postural tachycardia. In some patients with medication-resistant POTS and neurally mediated hypotension, intravenous saline has been used as an effective therapy. In our patient population with both migraine and POTS, we observed that treatment of POTS with high sodium and fluid intake and pharmacotherapy, which often includes a low dose of a beta blocker in combination with fludrocortisone (an aldosterone analog that increases plasma volume through enhanced sodium resorption), can also improve headache frequency and severity. Conversely, when we effectively manage chronic migraine with prophylactic headache therapy, symptoms of POTS tend to concurrently improve. This correlation between migraine and POTS response to treatment points to potentially common pathophysiology and underlying mechanisms for both disorders. We believe that in the Pogoda et al study, patients who consumed a high sodium diet, whether by coincidence, preference or perhaps by noticing a beneficial effect on their symptoms, had lower migraine frequency as a result of the increased sodium consumption. This effect may be especially significant in women with lower body mass index (BMI), as the study confirmed, who tend to have lower blood pressure than women with normal or high BMI. The most plausible hypothesis is that decreased sodium consumption results in decreased plasma volume, which is then sensed by the cerebral vasculature, similarly to sensing changes in the barometric pressure or low blood glucose level. This decreased plasma volume – hypovolemia – may act as a possible precipitating factor in the