Three consecutive studies on the effects of horsetail extract

Common horsetail extract is shown to interfere with cells responsible for an immune response.

Equisetum arvense, better known as common horsetail, is frequently used by patients with inflammatory immune disorders. It is a phytotherapeutic herbal substance, whose possible medicinal effects are supported by a number of studies. Amongst others, it appears to have anti-inflammatory properties, without the side effects that the effective conventional medications (immunosuppressants, for example) may have.

This research investigated the impact of this herbal extract on lymphocytes involved in inflammatory immune processes. The experiments showed that common horsetail extract is able to inhibit cell division of lymphocytes. One of the responsible mechanisms appears to involve partial inhibition of lymphocyte activation. In addition, the production of mediating substances (tumor necrosis factor-alpha and interferon-gamma) by lymphocytes was also found to be slightly inhibited.

This means that the horsetail extract interferes in various ways with immune cells, which may explain its traditional use in treatment of inflammatory disorders.

(Source: BMC Compl. Alt. Med. 2014)

Common horsetail: its anti-inflammatory effect is more than just active silica.

Equisetum arvense L., known as common horsetail, is officially registered to be used as internal application for inflammatory diseases of the urinary tract and external application for treatment of poorly healing wounds.

It is one of the oldest plants on earth and has the highest concentration of silica among plants. As silica content can be as high as 25% of the dry weight of the plant, this could be the active component responsible for the medical properties of horsetail. 

This study investigated a method for preparation of a high-concentration-silica solution. In an in vitro model the researchers looked at the effect of such a standardized silica solution and horsetail preparations on human immune cells. They also searched for other possible effector molecules, contained in the horsetail preparations.

So called horsetail decoction for 30 minutes at 90°C appeared to be superior in providing high concentrations of soluble silica. The immunosuppressive effects of this preparation on specific immune cells, was compared to those of a silica standard solution. The results lead to the assumption that the known anti-inflammatory effects of this herbal remedy are at least partly mediated by silicon.

As plant extracts consist of many different components, the possible presence of other active substances in the horsetail extract was investigated. Secondary plant compound profiles of the different time-dependent horsetail preparations were compared. After four hours of decoction isoquercitrin was by far the most abundant flavonoid present, which is a molecule with anti-oxidant activity and anti-inflammatory properties. These results suggest that both silica and isoquercitrin are at least partly mediating the observed anti-inflammatory activity of horsetail.

(Source: Planta Med 2018)


Silicon absorption from high-concentrated horsetail preparations.

Although silicon is the second most abundant element in the earth’s crust, it’s only a trace element in higher living organisms. Human daily intake varies greatly, and official reference ranges have not been established. Its function remains unknown. High concentrations are found in common horsetail (Equisetum arvense), which is a herbal remedy plant. It is said to be of help in case of urinary tract (minor) problems and superficial wounds. In folk medicine its tea is used as supportive treatment for chapped nails, loss of hair and inflammatory immune diseases. In anthroposophic medicine it is applied for treatment of kidney disease and rheumatoid arthritis.

Research showed possible anti-inflammatory effects of this tea, however clinical studies on this are rare. Hence this study, in which the goal was to investigate oral silicon uptake via a special preparation, and to determine whether this can be safely and effectively used to have an immunosuppressive effect. As far as we know, this is the first study where this has been investigated.

Twelve healthy volunteers were grouped in three different protocols, that varied in their intake of silicon. The three levels ranged from (silicon-low) water intake, normal equisetum preparation levels, and an extra high concentrated preparation that contained almost four times more silicon than the normal preparation. After three days on a silicon -low diet, participants ingested the allocated water or preparation, on three successive days, all at the same time during the day. Most important to know was the plasma silicon concentration in the participants on high concentration preparation. Furthermore, other measurements were performed to learn more about the behaviour, effect and safety of silicon in the human body.

The outcome of this study is that normal dose common horsetail preparation is safe and well tolerated, whereas the high concentration is safe, though less well tolerated, causing abdominal pain and diarrhoea. A significant rise in serum silicon after drinking normal horsetail preparation was seen. Urinary secretion, but not the serum accumulation, was elevated in the high concentration group. In terms of safety, none of the preparations showed an effect on immunity parameters, nor was there a visible pharmacokinetic effect. It could be that both the serum concentrations and the duration of the time that these kinetic parameters were followed, were too low and too short, respectively. Another reason for the lack of a clear effect, could be that the participants were healthy, and so their immune system is supposed to be healthy and equilibrated too. Perhaps an overreactive immune system is a prerequisite for showing an effect of this treatment with common horsetail preparation.

(Source: Planta Med 2021)