1. INTRODUCTION

Humic substances (HS) are straw-colored organic acids mainly derived from soil humus and plants. They have unique properties of exhibiting hydrophobic core and hydrophilic exterior. The major components are humic acid (HA) and fulvic acid (FA). FA is a category of HS with low molecular mass, constituting a short-chain compound that dissolves in acid or base solutions (Table 1). It comprises functional groups, such as carboxyl, phenol, hydroxyl, amine, and quinine groups, exhibiting a high complexation capacity with heavy metals (Zhong et al., 2023). HA, with a comparatively higher molecular mass, dissolves in alkaline pH and possesses several nutraceutical (NC) properties, including anti-inflammatory, antimicrobial, and immune regulation abilities.

Humic substances exhibit favorable impacts on plant physiology by enriching soil structure and fertility, impacting nutrient uptake and root architecture. HS are the massive constituents of soil organic matter (~60%) and are speculated to be a key ingredient of the terrestrial ecosystem. It is responsible for various complex chemical reactions that occur in the soil. One of the notable traits of HS is their capability to interact with metal ions, oxides, hydroxides, minerals, and

organic compounds, comprising toxic contaminants. The sources of HS are peat, lignite, leonardite, coal, and natural water sources, such as rivers, lakes, and streams.

Unlike other natural ingredients, the journey of HS, for example, HA and FA, as human healthcare products has been remarkable. In ancient times, HS was used as a drug in different systems of medicines that still exist in indigenous medicine streams, such as Unani (Perso-Arabic Medicine) Ayurvedic (ancient/traditional Indian system), Chinese (Zhou et al., 2014), Russian (Schepetkin et al., 2003), and other countries of the Himalayan region. With the progression of time and scientific temperament, the evidence or science-based medicine (e.g., allopathic medicine) took over, as the natural ingredient-based medicines lacked sufficient scientific evidence. Other than uses in indigenous systems of medicine, it is also being explored in other facets of healthcare. In the given scenario, HS products have following four options

Figure 1

A pictorial presentation of all the available non-prescription HS-based products (dietary supplements and cosmetics/topicals). Each region is divided into three colors—blue (liquid oral HS products), green (solid oral HS products), and yellow (topical HS products). The area of any colored region is an approximate representation of percentage of that category of HS product in the particular region. For example, in Australia, almost all the HS products are of liquid oral category.

Humic substances have the potential to be explored in all four categories, which is not a common phenomenon for all natural ingredients. Table 6 provides a list of some natural ingredients being explored in different categories. There are around 150 dietary DS-based products available globally, and research is being conducted to establish their safety profile and efficacy. Furthermore, it is also marketed as veterinary products, a unique aspect of HS, compared to other natural remedies. Its exploration as a pharmaceutical excipient is still under investigation. However, the journey so far and the way forward is not as simple as it appears. There are several reasons why HS are not explored extensively so far; this could be due to expensive raw materials (i.e., shilajit of Himalayan regions), structural complexity, and physicochemical properties (Gnananath et al., 2020). The manuscript discusses the challenges in acceptance of HS as healthcare products (prescription or dietary supplement category) generally asked by the stringent regulatory authorities worldwide. Despite successful sales as DS in the European Union (EU), United States, Commonwealth of Independent States (CIS) region, and Australia, the industry still faces tough questions during the approval (marketing authorization) process. The HS industry faces difficulties, unlike the pharmaceutical industry, because DS or NC marketing authorization in one country is difficult to be accepted as a reference for another region, although it supports the application.

2. MATERIALS AND METHODS

This study includes an extensive literature search (using different search engines, such as PubMed, Web of Science, Science Direct, Scopus, Embase, Google Scholar, and Ovid), company and regulatory agency’s websites, and personal experiences in dealing with regulatory agencies during product approval.

3. HUMIC SUBSTANCES IN INDIGENOUS MEDICINE

Traditional or folk medicine is an indispensable facet of the global healthcare system. Its practices, passed down through generations, have proven to be effective in treating a myriad of ailments (Hill, 2009). From herbal remedies to acupuncture, traditional medicine offers an alternative to conventional treatments, and it has been an integral part of healthcare for centuries (Yuan et al., 2016). Therefore, it is important to embrace and respect the value of traditional medicine in order to provide holistic healthcare to all individuals. Indian traditional and folk systems, such as Ayurveda, Unani, Siddha, acupuncture, yoga, and indigenous therapies, are highly effective (Rizvi et al., 2022). According to the World Health Organization (WHO, 2023), an overwhelming number of countries, or 88% of the 170 member states, use traditional medicine.

Shilajit is used in the Indian subcontinent’s traditional medicine as a rejuvenator and an adaptogen (Andrade et al., 2023). It is also known as mumie, mumijo, asphaltum, punjabinum, arakul dshibal, and Hajar-ul-musa. In traditional medicine of Tibet, it is called zhaxun, meaning the “Juice of rock” or “the essence of rock” (Frolova & Kiseleva, 1996). The word “shilajit” is derived from two Sanskrit words: shila, meaning rock, and jeet, meaning win, which collectively means “conqueror of mountains” and “destroyer of weakness.” According to old traditional healers, there is hardly any curable disease that cannot be controlled or cured with shilajit (Agarwal et al., 2007). Shilajit is predominantly composed of paleohumus (80–85%), defined as “fully decomposed organic matter,” mainly derived from fossils that have been present inside the layers of rocks for many years, subjected to high temperature and pressure, ultimately metamorphosing into this material (Ghosal et al., 1997). It loses its viscosity in the summer season and oozes out from the rocks.

Chemically, shilajit contains gums, albuminoids, traces of resin and fatty acid, and a large quantity of benzoic and hippuric acids and their salts. The main active substances among all the medicinal compounds present in it are benzoic acid and benzoates (Kamgar et al., 2023), including bioactive oxygenated dibenzo-α-pyrones, tirucallane triterpenes, phenolic lipids, and small amount of tannoids. Shilajit, obtained from different sources, is a complex heterogeneous mixture, rather than a well-defined natural product and has varying amounts of both FA and HA as well as other compounds; although the overall structures of these compounds are poorly defined. However, now it has been standardized on the basis of its major organic constituents that shilajit mainly includes organic matter, HA, FA, and volatile and fat soluble components (Ghosal et al., 1995).

In the given manuscript, two major Indian systems of medicine (Ayurveda and Unani) are included. Shilajit, a major raw material of the Indian subcontinent, mainly contains HS. Globally, FA is often extracted from other deposits, such as peat lignite, leonardite, and coal. On the other hand, FA is also found in natural water sources, such as rivers, lakes, and streams.

As a prescription product, also known as a prescription medication or drug, shilajit is legally available only with a valid prescription from a licensed healthcare professional. Such medications are typically regulated by health authorities to ensure their safe and appropriate usage. Shilajit is the only humic substance used in different products of Indian system of medicine. The products are included in the formulary and pharmacopoeia of indigenous medicines (see Tables 7 and 8).

4. HUMIC SUBSTANCES AS DIETARY SUPPLEMENTS IN GLOBAL MARKET

DS or NC are included in the category of non-prescription products. They have no label claims for any therapeutic activity and are sold without prescription (a type of over-the-counter [OTC] products). This is the most common category of HS-based products and are available globally and even in some of the most stringent regulatory framework countries. Companies in this category typically operate on a small scale. The products are available in the form of oral solids (tablets, capsules, caplets, bars, and powder), oral liquids (solution and suspension), and topical products. Table 3 and Table 4 present some surprising facts about the available products, such as the following:

There is a significant variation in the dose of HS up to 4.8-g FA per day for adults to 300 mg for children.

There is a substantial variation in the regimen of consumption. The recommended regimen is up to 6 months in some orally consumed products, while in some labels, the recommended duration hasn’t been mentioned, allowing usage for unlimited period.

There is no quantification of HS in some of the products, and the daily intake of HS is not quantified for both adult and children.

5. ROLE OF HUMIC SUBSTANCES AS COSMECEUTICALS

Cosmeceuticals are the cosmetics exhibiting medicinal properties because of the existence of bioactive components corresponding to medicinal benefits (Choi & Berson, 2006). The distinct comparison between an inert cosmetic and a cosmeceutical can be relatively befitting, as an inert cosmetic is meant for aesthetic augmentation and quality enhancement whereas cosmeceutical is perceived for pharmacological healing (Kligman, 2000).

Humic substances have immense therapeutic potential, and hence cosmetics that include HS fabricate a significant proportion of cosmeceuticals. Globally, products constituting a specified combination of salicylic acid and HA in face cleansing and peeling creams serve manifold purposes, with skin enhancement being main function. The role of HS as bio-fertilizers and shoot growth-promoting agents is also worth acknowledging. HS are also often combined with herbal phytoconstituents, such as aloe, apple cider, and epigallocatechin-3-gallate (EGCG), to constitute veterinary and infant cosmeceuticals that have wide applications across the globe. Advantages of HS in skin care are as follows:

Today, mud, mineral and peat baths, as well as various natural packs and face masks, are offered in spas and wellness centers worldwide. Balneotherapy (a traditional bathing therapy) involves immersing a subject in natural mineral water or mineral-laden mud. The active substances in these mud baths are HS. For this reason, interest has increased in the use of HA and FA in dermatology and cosmetics.

6. HUMIC SUBSTANCES IN MODERN MEDICINE

Carbohydrate-derived FA (CHD-FA) is one of the products of this category that has undergone clinical trials to establish safety and efficacy for the topical treatment of eczema/dermetitis. Preclinical safety and efficacy data are available for this product with different indications. Manufacturers claim it to be a better FA than the naturally obtained HS. However, researchers working on HS find it debatable to be called CHD-FA, as the process of obtaining it does not adhere to widely accepted definitions.

Several clinical trials have been conducted and are ongoing to prove the therapeutic efficacy and potential of HA and FA (Table 9). An investigational randomized, double-blind clinical trial, comprising 15 males, was conducted to evaluate comparable efficiency with a placebo as a control measure for the treatment of erectile dysfunction and to enhance sexual libido. Results of the study showed an improvement in the sexual health scores as well as augmentation in sexual quality score (NCT02794454) (Sandip & Shirish, 2016).

An interventional study intended to assess the effectiveness of shilajit pill in sexually active married women was conducted in Tarbiat Modares School of Medical Sciences, Nasr, Tehran. Its results were based an the analysis of a list of questionnaires (IRCT20200617047808N1) (Mosavi et al., 2023). This study concluded that Shilajit pills significantly improved sexual function in sexually active married women but did not have a significant effect on their overall sexual quality of life. In Japan, a novel exploratory clinical trial focused on identifying the effects on sustained intake of FA (UMIN000041443) (Mitsuko, 2020). Germany and Austria collaboratively conducted a randomized clinical trial on irritable bowel syndrome and the consequence of utilizing HA as a clinical intervention (DRKS00005183) (Haufe et al., 2021). Both these trials focused on the health effects of sustained intake or intervention with specific agents (FA and HA). The Japanese trial was exploratory and targeted general health parameters, while the German-Austrian trial was randomized and focused specifically on IBS. Both these trials showed positive, statistically significant outcomes for their respective interventions.

In India, a clinical investigation was carried out on HIV+ patients to study the effects of extended self-administration of CHD-FA wellness drink on HIV (CTRI/2012/01/002324) (Botes et al., 2018) study revealed that HIV+ patients safely and tolerably self-administered the CHD-FA wellness drink over an extended period. A randomized placebo-controlled, double-blind clinical study was conducted in India on shilajit for the management of diabetic polyneuropathy to substantiate the hypoglycemic potential of HS (CTRI/2012/06/002712) (Baghel, 2012) and showed that shilajit can be utilized for diabetic polyneuropathy and found it significantly improved blood glucose control and neuropathic symptoms when compared to a placebo.

A study in India was jointly conducted by Sawai Man Singh Medical College, Jaipur, and the National Institute of Ayurveda, Jaipur, to determine the impact of shilajit on the blood chemistry of healthy human volunteers. The results showed that administering 2 g of shilajit for 45 days did not significantly affect physical parameters, such as blood pressure, pulse rate, and body weight, nor did it caused any changes in hematological parameters. There was a significant reduction in serum triglycerides and serum cholesterol, accompanied by an improvement in high-density lipoprotein (HDL) cholesterol levels. Additionally, shilajit enhanced the antioxidant status in all participants. The study’s results suggested that shilajit has hypolipidemic and potent antioxidant properties (Sharma et al., 2003).

Multiple clinical trials have been conducted to validate and evaluate the effects of FA on male sexual health, and the ability of such compounds to treat male infertility and associated conditions, such as oligozoospermia and erectile dysfunction. Traditionally, it has been witnessed that HS, mainly FA, are employed in the treatment of arthritis and other bone ailments. Clinical trials were conducted to authenticate the osteo-strengthening therapeutic potential of HS compounds. Intricate elucidation of these clinical trials are provided in Table 9.

FA possesses different properties that can be exploited as excipients in conventional and novel drug delivery systems (such as 505(b)(2) application to the US Food and Drug Administration [US FDA] and hybrid application to the European Medicines Agency [EMA]). There are some literature reports of FA exploration in drug delivery (Mirza et al., 2011c, 2016). The impediments encountered and the solutions are discussed in Mirza (2018).

7. GLOBAL PATENT STATUS OF HUMIC SUBSTANCES

The therapeutic potential of HS is widely directed globally. HS are efficiently used as skin cleansing and acne-preventive agent, patented (CN/1219507/C) by Xuesong et al., 2005. it is also used in hypoglycaemic preparations (e.g., sodium fulvate) and oral hygiene products (e.g., FA), patented (CN/101744844/B) by Baocai et al., 2012. The most crucial implication of HS in the current scenario is their inclusion as active NC formulations, either singly or in combination with other immunity-enhancing food supplements with disease preventive actions, as observed in ashwagandha- and shilajit-patented formulations. FA itself is elucidating the complications of systematized drug delivery. Purified FA is used as a carrier in the formation of a patented water-soluble drug delivery system (shilajit formulation; EP/3672578/A1) (Roger et al., 2020). Along with the amalgamation of Chinese medicine, edible-grade FA and excipients, a patented FA beverage is developed with multifactorial advantages, such as enhancing immune response and heart health, lowering of blood glucose levels, etc. (CN/103564587/B) (Min and Huifen, 2015). This patented adaptogenic herbal chewing gum comprises shilajit, ashwgandha, citrulline malate, Siberian ginseng, L-tyrosine, Ganoderma lucidum (Reishi), Hericium erinaceus (Lion’s mane), coconut oil, and resveratrol, and has multiple health benefits (Roger et al., 2020). The epidemiological cluster accessing such products can be authenticated by intricately introspecting patent information as well as marketing data. An elaborate description of several such essential patents is given in Table 10.

Overall, the reviewed trials highlight a variety of potential applications of HS, particularly shilajit and FA. Most studies report positive outcomes in the areas such as bone health, sexual functioning, digestive health, and muscle performance. The future clinical trials should focus on larger sample sizes, diverse populations, and longer follow-up periods to confirm the efficacy and safety of these substances, ensuring their reliable integration into therapeutic practices.

8. COSMETIC AND PHARMACEUTICAL APPLICATIONS OF HUMIC SUBSTANCES

The most widely used category of HS is DS or NC. In countries where HS are neither indigenous nor part of the traditional system of medicines, HS products in the market face some common regulatory queries as mentioned in Section 10. The exporters to these countries also encounter queries on similar lines. The earlier studies (Jain et al., 2020; Khan et al., 2022; Mirza et al., 2011a; Mirza et al., 2011b) have demonstrated that both FA and HA function as solubilizing agents by condensing pharmaceutical and cosmetic-active ingredients within their micelle-like structures. These structures, with their core voids, enhance water solubility through the formation of inclusion complexes. Additionally, the phenolic groups present in HS act as electron donors, neutralizing free radicals and preventing chain reactions (de Melo et al., 2016). These antioxidant and solubilizing properties of HS make them valuable constituents of both cosmetic and pharmaceutical industries. Similar to β-cyclodextrin, HS also contain void spaces and can form inclusion complexes. As a result, our research team also developed a ternary complex involving hydrolyzed Bacopa monnieri, FA, and hydrogenated soy lecithin to improve the entrapment efficiency of phospholipid complexes, akin to the drug-in-cyclodextrin-in-liposome system (Gnananath et al., 2022).

9. EXPLORING THE IMPACT AND MECHANISM OF HUMIC SUBSTANCES ON HUMAN HEALTH AND AGRICULTURE

Humic substances are vital organic compounds found in both terrestrial and aquatic ecosystems, playing a crucial role in environmental sustainability and contributing to animal and human well-being. Their complex structures and formation processes influence various functions, including nutrient cycling, metal ion mobilization, soil fertility, and pollution management. In addition to their environmental significance, HS have shown potential health benefits, such as enhancing gut health and supporting detoxification processes. As mentioned previously, understanding these substances requires a cross-disciplinary approach, involving expertise in humic chemistry, regulatory affairs, and product development to effectively apply them as excipients or NCs (Gnananath et al., 2020). Ongoing research in biochemistry, molecular biology, and environmental science would undoubtedly enhance our comprehension of HS, highlighting their essential role in balancing of the ecosystem and in promoting both animal and human health.

10. GENERAL REGULATORY QUERIES ASSOCIATED WITH HUMIC SUBSTANCES

Some common regulatory queries are mentioned below.

Some of the above-mentioned queries are easily addressed (in a cost-effective manner) by generating quality-related data (i.e., in vitro data); however, safety and efficacy establishments require a full battery of studies on animals (in some cases humans too), which is undoubtedly a major investment. DS- or NC-based companies have their own apprehension about investment, primarily considering the size of the business involved. One major concern is the lack of quality standards, specifications, or monographs of HS for human-grade products. Their absence hinders the growth of natural HS in the realm of human-grade products. Some regulatory agencies also request a complete list of ingredients present. While intentionally added ingredients are generally fewer, the associated complexes/minerals/elements are numerous. Though the complete list of analysis can be given to the agency as a one-time report, companies refrain from including it in batch release specifications or certificates of analysis because it may increase production cost, ultimately affecting the retail price of final product. The analysis and quantification of HS is itself a challenging task. The Lamar method is a well-accepted method (Lamar et al., 2014) for quantification, but it is time-consuming and the availability of DAX-8 resin is not so easy to come by. There are technical challenges in developing chromatographic or spectroscopic quantification methods for HS.

The good part is that HS-based research is in progress globally. A well-coordinated effort may address the issues more efficiently. If a sound regulatory strategy is drawn (such as 505(b)(2) application of the US FDA), the bridging data can be generated between different datasets available in public domain, and strong safety and efficacy claims can be established, which is definitely a multidisciplinary assignment. Global organizations, such as International Humic Substances Society and Humic Products Trade Association, can take a lead in channelizing global efforts. Considering the inherent variability observed in materials, specifications can be categorized into different grades and sub-grades.

11. CONCLUSION AND EXPERT PERSPECTIVES ON HUMIC SUBSTANCES

Undoubtedly, although HS have achieved great success in irrigation as fertilizers and for soil health, and their various pharmacological or therapeutic potentials for human health are to be explored. This review synthesized the current state of research on HS, providing insights into their applications across multiple industries. However, so far, the success is not up to expectations. The reason definitely lies in the complexity of the moiety and lack of well-coordinated efforts. In general, the commercial players involved are small business groups, and funding for its research is also an impediment. There are examples where a substance can be successfully explored if experts from regulatory, analytical, pharmacology, and chemical science are brought together. In case of lack of funds, a long-term strategy can be chalked out, and academia and non-profit organizations can be brought on board. However, the responsibility to execute the strategy should lie with a particular group or organization.

This review compiled the most significant findings from clinical studies and highlighted key patents, illustrating innovative applications that showcase HS as potential bioactive agents. By addressing both therapeutic and commercial potential of HS, this review aspired to foster cross-disciplinary collaboration among scientists, healthcare professionals, and industry stakeholders. The consolidated information presented here underlines the need for continued research to unlock the full potential of HS, paving the way for new, safe, and effective products in the health and wellness sectors.

AUTHOR CONTRIBUTIONS

Mohd. Aamir Mirza: research concept and design, data analysis and interpretation, and writing of the article; Rajat Goel and Somaan Lareb: collection and/or assembly of data; Uzair Ali: writing of the article; Aslam Siddiqui: data analysis and interpretation; Zeenat Iqbal: critical revision of the article; Kattamanchi Gnananath: data analysis and interpretation, and critical revision of the article; Mohammed Aslam: writing of the article; Noor Alam: data analysis and interpretation; and Vinay Bharadwaj Tatipamula: writing and critical revision of the article. The final manuscript was verified and approved by all the authors.

CONFLICT OF INTEREST

The authors declared no conflict of interest.