Updated: Sep 2, 2019
In a fairly recent study, researchers sought to find out whether or not ascorbic acid or vitamin C status was related to symptom severity in various allergy-related conditions. In addition to specific symptoms (e.g. rhinitis, pruritus, etc.) in these allergy-related respiratory and cutaneous conditions, namely asthma, allergic rhinitis, and atopic dermatitis or eczema, they also evaluated for non-specific symptoms. This included fatigue, sleep disorders, depression, and lack of mental concentration. Before I discuss the key findings of this study in further detail, we need to briefly review some background information regarding the pathogenesis and treatment of allergy-related conditions. Specifically, we need to review a few relevant details regarding reactive oxygen species, histamine, and vitamin C.
The Roles of Reactive Oxygen Species and Histamine in Allergy-Related Conditions
We now know that oxidative stress plays a key role in the pathogenesis of asthma, allergic rhinitis, and atopic dermatitis. [1,2] Although reactive oxygen species’ primary purpose is to help eradicate invading pathogens, they tend to promote pro-inflammatory states within the body. This is particularly relevant to individuals with allergy-related conditions.
In individuals with these conditions, the reactive oxygen species, in conjunction with the pro-inflammatory state that they induce, appear to trigger the production and release of histamine from mast cells and/or basophils. [3,4] Because of histamine’s role in increasing inflammation and capillary permeability as a part of this allergic/immune response, the extent of histamine release is directly proportionate to the severity of many symptoms in these allergic conditions.
In other words, reactive oxygen species lead to the release of histamine, and more histamine means more severe allergy-related symptoms.
The Effect of Dietary Histamine on Symptom Severity in Allergy-Related Conditions
In addition to being produced within our bodies, we also find histamine in a variety of foods. Histamine content is especially high in alcohol and other fermented beverages, processed and smoked meats, and in foods that are processed by bacteria, such as cheeses, yogurt, and sauerkraut.
Evidence suggests that symptom severity in some allergic conditions may also be linked to dietary histamine intake. In other words, those who consume diets high in histamine-rich foods are likely to have more severe specific and non-specific allergy-related symptoms. This may be because, although as humans we produce an enzyme called diamine oxidase that helps us break down excess dietary histamine, some people have lower amounts of this enzyme and are unable to efficiently break down excess histamine.
In fact, the authors of one case study suggested that there may be a subgroup of individuals with atopic dermatitis who demonstrate allergy-like symptoms but whose food allergy tests repeatedly come back negative. Researchers reported that maintaining a balanced, low-histamine diet may be helpful for such individuals with atopic dermatitis, while consuming histamine-rich foods may lead to an aggravation of symptoms. 
Vitamin C’s Effect on Histamine
Vitamin C is a potent antioxidant; therefore, it protects against oxidative stress. As such, increasing the concentration of ascorbate in the plasma is a method that is frequently employed in order to decrease oxidative stress and inflammation. Research also demonstrates that vitamin C has a significant histamine-reducing effect  and that, conversely, low vitamin C levels tend to result in an exponential increase in histamine. As we’ve discussed, higher histamine levels tend to result in increased symptom severity. Because of the roles of reactive oxygen species, inflammation, and histamine in allergy-related conditions like asthma, allergic rhinitis, and atopic dermatitis, the benefits of vitamin C that we’ve discussed are highly relevant to our patients with these conditions.
If we choose to use vitamin C therapeutically with these patients, it should be administered in a very specific way. Because the body places limitations on how much vitamin C can be absorbed and transported when consumed orally, plasma concentrations cannot be sufficiently raised by these means; the plasma concentration of ascorbate can only be sufficiently elevated by intravenous administration of the vitamin. 
[If you would like to learn more about how you can incorporate IV nutrient therapy into your practice to address a variety of health conditions, click here to learn more about the IV Therapy Academy.]
Study Findings: How Vitamin C Levels Affect Symptom Severity in Asthma, Allergic Rhinitis, and Atopic Dermatitis
The connection between oxidative stress, inflammation, and symptom severity in asthma, allergic rhinitis, and atopic dermatitis is difficult to deny. As such, the need for therapies that offer potent antioxidant, anti-inflammatory, and anti-histamine effects is clear. One such therapy, Vitamin C, when administered intravenously, leads to an increase in plasma ascorbate and, consequently, a reduction in symptom severity. 
Now, here are the key findings from the study I referenced at the introduction of this article:
Both study participants who were taking allergy-related medication and those who were not (other than the IV vitamin C, of course) experienced similar percentages of improvements in their symptom scores
IV vitamin C led to more significant improvements in chronic non-specific symptoms (again, these are fatigue, poor concentration, disturbed sleep, and depression), compared to acute non-specific symptoms
The higher a study participant’s baseline histamine levels were, the more pronounced the reduction tended to be after administration of IV vitamin C
In addition to these findings, the data suggested that many individuals with allergy-related conditions may actually have low vitamin C levels to begin with, and that correcting these values may result in significantly decreased symptom severity. If you would like to learn more about how you can incorporate IV nutrient therapy into your practice to help your patients address a variety of health conditions, click here to learn more about the IV Therapy Academy.
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Chung BY, Cho SI, Ahn IS, et al. Treatment of Atopic Dermatitis with a Low-histamine Diet. Ann Dermatol. 2011;23 Suppl 1(Suppl 1):S91–S95. doi:10.5021/ad.2011.23.S1.S91
Hagel AF, Layritz CM, Hagel WH, et al. Intravenous infusion of ascorbic acid decreases serum histamine concentrations in patients with allergic and non-allergic diseases. Naunyn Schmiedebergs Arch Pharmacol 2013; 386: 789–793.
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Vollbracht C, Raithel M, Krick B, Kraft K, Hagel AF. Intravenous vitamin C in the treatment of allergies: an interim subgroup analysis of a long-term observational study. J Int Med Res. 2018;46(9):3640–3655. doi:10.1177/0300060518777044