Cadmium in herbal weight loss products as a health risk factor for consumers

Consumers perceive the intake of dietary supplements as a rapid and easy way to reduce body weight without having to change the diet. The world market for dietary supplements offers a number of herbal remedies, including those that support weight loss [1, 2]. Such products are among the most popular dietary supplements available on the Polish market. They are ranked in eighth place among the most commonly chosen products of this type in Poland and account for approximately 4% of the domestic market for supplements [3]. The widespread use of dietary supplements results partly from the increase in consumer awareness of the influence of diet, absorbable vitamins, and micro- and macroelements on health. Advertisements and commercials for products that promise immediate weight reduction have an unquestionable impact. These products are a response to the expectations of today’s society in terms of esthetics of external appearance [1, 2].

Herbal dietary supplements, which affect the process of weight loss, accelerate fat tissue reduction, cleanse the body of toxins, inhibit appetite, act as diuretics, regulate digestive processes, and reduce fat absorption [4]. The composition of raw materials of weight loss dietary supplements is considerably varied. Herbal mixtures containing such plants as couch grass rhizome (Graminis rhizoma), chamomile (Chamaemelum), white mulberry (Morus alba), field horsetail (Equisetum arvense), common dandelion (Taraxacum), or senna are the most frequently used to produce such supplements. Herbs can have a beneficial effect on the functioning of the human body. However, various toxic substances (e.g., toxic metals) are absorbed by these plants due to progressive environmental pollution. Such pollution is the main cause of heavy metal contamination of herbal plants that are used in the production of herbal remedies. Soil, which accumulates heavy metals, is an environmental element that plays a crucial role in cadmium contamination in plants [5, 6].

The most significant sources of cadmium emissions in the environment include anthropogenic sources such as nonferrous metal ore mining and processing industries, energy and chemical industries, transport, landfill sites, and burning of fossil fuels. Natural sources of toxic metal emissions in the environment include forest fires and volcanic eruptions. The use of plant protection products and mineral fertilizers, especially phosphate fertilizers, as well as sludge from sewage treatment plants may also affect cadmium contamination of soil [7, 8].

Ingestion of contaminated food is the major source of cadmium intake for the general population. The food products with the highest contribution to cadmium exposure are the edible plants. The gastrointestinal absorption of cadmium in humans amounts to about 5% but may be increased in iron-deficient people and can reach 15–20% [9]. The research has shown that bioavailability of cadmium from drinking water and food is not significantly different in the gastrointestinal tracts of rodents. Therefore, there is probably little difference in the human bioavailability of cadmium in food and drinking water [10]. The human exposure to cadmium can cause various adverse health effects such as kidney dysfunction, bone effects (osteoporosis), lung diseases, and liver and reproduction disorders. In 1993, the International Agency for Research on Cancer (IARC) classified cadmium and cadmium compounds as group I human carcinogens. The long-term exposure to cadmium may be associated with incidence of various cancer types: breast, lung, prostate, testes, pancreas, and kidney cancers [11, 12, 13].

The aim of the study was to assess the content of cadmium in selected herbal weight loss products available on the Polish market in terms of exposure of consumers of herbal infusions from the analyzed products and the related health risk.

The study found a similar contamination of dried mass of herbal weight loss products that were registered as dietary supplements compared to other analyzed herbal weight loss preparations. The latter group included products registered as foods intended for particular nutritional uses (e.g., dietary foods for special medical purposes and foods for people with carbohydrate metabolism disorders) and products introduced to the market as food that have not been classified yet as foods intended for particular nutritional uses or dietary supplements. The dietary supplements and the other herbal preparations are not medicines and therefore they are not subject to the same testing, manufacturing, and labeling standards and regulations as drugs. For this reason such products present a chance to pose a health risk for consumers because of contamination with heavy metals.

In the study, the presence of cadmium was found in the dried mass of most herbal preparations, which confirms the bioavailability of cadmium to plants [16]. Furthermore, despite the fact that cadmium is absorbed from the soil mainly by the root system of the plants, the metal is frequently accumulated in the upper parts of plants (i.e., seeds, leaves, inflorescences) [17], which are often used for the production of herbal remedies.

From the perspective of consumer exposure to heavy metals, their concentration in the infusion is of crucial importance. In the study, cadmium was found in most herbal infusions regardless of whether they were classified as dietary supplements. The products whose main ingredient was hibiscus were the herbal remedies with the highest cadmium concentrations (Supplementary material 1). Literature data confirm that hibiscus is pre-disposed to accumulate cadmium. As a result, the plant can be used in the process of phytoremediation of soils contaminated with heavy metals [18]. Although the above studies used another species of hibiscus (Hibiscus cannabinus), Hibiscus syriacus is used for the production of herbal remedies. However, both species belong to the same genus and show similar physiological properties.

Some herbal mixtures whose main ingredient was yerba mate or bladderwrack were also among the remedies (infusions) which were most heavily contaminated with cadmium. The former plant is a bush from South America. Its leaves are used to prepare a tea known as mate. Barella et al. reported that one of the highest concentrations of heavy metals was found in dietary weight loss supplements containing yerba mate [19]. The source of cadmium in herbal leaves may be related to artificial fertilizers, plant protection chemicals containing the metal, and possible contamination of soils caused by industrial activities, as in the case of tea leaves [20, 21, 22]. The latter plant (bladderwrack) is a brown alga which occurs, for instance, in the Baltic Sea.

Since algae, including bladderwrack, have a high capacity to accumulate heavy metals [23], the quality of the environment from which they are obtained is of great importance. Cadmium contamination of water reservoirs may contribute to the high content of this metal in algae-based herbal products. Compared to other dietary supplements, a threefold higher value of maximum allowable concentrations of cadmium in the products showed higher cadmium concentrations in dietary supplements which contained algae-based products [15].

The content of heavy metals in herbal infusions is influenced by the level of contamination of the dried mass and the composition of the herbal mixture. The pH of the infusion is an additional determining factor. It has been shown that the acidification of the solution significantly increases the migration of metals from the dried mass to the infusion: for instance, as a result of adding citric acid to tea infusions [24]. It was found that the brewing time may also affect the level of cadmium extraction from the tea infusion. Sedrowicz et al. showed that the highest cadmium concentration was reached after 20 minutes of brewing [25].

In the present study, the estimation of the exposure of consumers of herbal weight loss products to cadmium was also conducted. The study considered three exposure scenarios for adults who consumed one to three standard servings per day. The amount of exposure to cadmium, and thus the health risk to consumers, increased with the increase in the consumption of herbal products. None of the herbal remedies under study provided the body with a sufficiently high dose of cadmium to create a significant health risk (HQ > 1).

In the case of the consumption of the most contaminated infusion, consumer exposure to cadmium accounted for approximately 50% of the reference dose. However, when four consecutive herbal products were consumed, the estimated exposure exceeded 40% of the safe exposure threshold. The results should be considered alarming because herbal weight loss products are only a supplement to the all-day diet. In general, herbal products are not regarded as the most important sources of human exposure to heavy metals. The highest doses of these products are delivered to the body by vegetables and cereal products [26]. This problem is particularly important in the cadmium-contaminated areas caused by industrial activity (e.g., the Silesian Province). It has been estimated that the consumption by the inhabitants of this region of only a few species of vegetables grown in the arable land located in the central part of the Silesian Province may be associated with a sufficiently high foodborne exposure to cadmium to pose a significant health hazard [27, 28]. Therefore, providing the organism with additional doses of cadmium in herbal infusions (which in most cases are not necessary for the proper functioning of the organism and result from striving for slimness) significantly increases the risk of adverse health effects caused by the toxic and carcinogenic metal.

In the context of the results of the study, which indicate the possibility of cadmium contamination of some herbal weight loss products, which significantly increases the health risk for consumers, it is essential to take appropriate prophylactic measures. The responsibility for the health safety of consumers lies largely with the manufacturers of such products, who should pay attention to the source of the raw materials used for the production of herbal remedies and their quality. Mixtures should be randomly inspected for heavy metals and other common contaminants such as plant protection chemicals. Studies should be combined with health risk assessment of potential consumers. Manufacturers must be aware which components of herbal products may potentially be the most important source of their contamination.

On the other hand, consumers themselves should be more cautious when deciding to use such herbal products. The ideal solution would be to consult a family physician who would assess whether the use of a particular product is beneficial or whether the patient could experience adverse effects (e.g., herb-drug interactions). Furthermore, it is important for consumers to be aware of the possibility of contamination of heavy metals in herbal products. There is a possibility of accumulation of doses due to exposure related to the consumption of food and the use of herbal products even in the case of concentrations that do not pose a health risk.

Unfortunately, individuals choose such products due to aggressive advertisements and commercials for herbal weight loss products, as well as the image of a slim figure created by the mass media. Therefore, it is warranted to introduce more restrictive legal regulations that could impose greater obligations on the manufacturers of herbal products in terms of ensuring the health safety of such products. On the other hand, both physicians and pharmacists should instruct patients more about the potential health risks associated with uncontrolled use of herbal products, including those resulting from excessive exposure to heavy metals. Therefore, it is advisable to conduct training courses dedicated to health care workers in this respect to broaden their knowledge so that they could use it in their contact with patients.

The content of cadmium in herbal weight loss products did not exceed the maximum allowable concentration. The exposure of consumers of the most contaminated herbal infusions to cadmium could be even equal to half of the reference dose, which is an acceptable exposure threshold. To ensure consumer health safety, manufacturers of herbal weight loss products should pay more attention to the quality of the raw materials, whereas consumers should be aware of possible health hazards arising from the use of such products.