The consumption of vegetable milk as a substitute for cow’s milk has increased in recent years. Of all the vegetable beverages on the market, soy is the most widely consumed. Soy is exposed to contamination by different chemical elements during harvesting. In this study, the concentration of fluoride in soy beverages was analyzed. Fluoride is an element that in high concentrations can be toxic, causing dental and bone fluorosis. The aims of the study were (i) to analyze the fluoride concentration in 30 samples in the most popular brands (A-Brand, B-Brand, C-Brand) of soybean beverages by a fluoride ion selective potentiometer and (ii) to evaluate the toxicological risk derived from its consumption. The fluoride concentrations were 15.5 mg/L (A-Brand), 11.3 mg/L (B-Brand) and 8.5 mg/L (C-Brand). A consumption of 1 to 3 servings/day was established. One serving (200 mL) of soybean beverage offered a contribution percentage over the ADI (acceptable daily intake) for infants and children. Teenagers and adults did not exceed the ADI (10 mg/day). The consumption of soy beverages contributes significantly to the daily intake of fluoride, which could exceed the ADI with a consequent health risk. It is recommended to control the fluoride levels in the raw material and in the final product to assure the safety of these products.
Vegetable beverages have been consumed throughout history as substitutes for cow’s milk. Vegetable beverages are extracts from legumes, seeds, cereals, etc. in water whose appearance resembles cow’s milk. There is a great variety, although soy drinks are the most consumed . Consumption and production of vegetable beverages have been increasing. According to an estimation made at the 38th National Congress of the Spanish Society of Primary Care Physicians (SEMERGEN) in 2016, global consumption of vegetable beverages will increase by 2.2%. However, in countries such as Spain, the increase is expected to be 15.8% .
The reasons why the consumption of vegetable beverages such as soybean beverages is increasing is mainly due to a rejection of dairy products due to lactose intolerance, allergy to cow’s milk proteins and/or cholesterol problems . In addition, in recent years, vegetable and plant sources (cereals and legumes) have been accepted as functional foods due to the presence of components that promote health benefits, which is favoring an increase in its consumption .
Soybean beverages, compared to other vegetable beverages, are most similar in terms of nutritional value to cow’s milk . However, cow’s milk is 15% and 10% richer in branched chain amino acids (BCAAs) and essential amino acids (EAAs), respectively. Although it is a good source of fiber, minerals such as Fe or Zn and certain vitamins, the bioavailability of calcium is lower, and it is not a good source of vitamin B12, among other vitamins [6,7]. Therefore, milk for infants or children should be supplemented .
Soybean is rich in polyunsaturated fatty acids (n-3 and n-6). Studies in experimental animals indicate that diets containing soybean beverages favor a reduction in high-density cholesterol (HDL) . It also contains potentially bioactive compounds such as phytoestrogens, which are associated with reducing the rates of breast, ovarian, prostate, colon cancer, etc. [10,11]. Although there are studies that link a high consumption of soybean with the risk of developing breast cancer in women with menopause , recent studies indicate that it reduces the risk and even improves the symptoms of menopause [13,14,15].
The increase in environmental pollution and its impact on crops, especially soybeans, constitutes a risk to consumer health. Soy is capable of absorbing potentially toxic elements [16,17,18]. Among the different chemical elements that can pose a health risk, it is worth highlighting the fluoride ion. Fluorine belongs to the group of halogens and is the most electronegative element in the periodic table, which gives it great chemical reactivity. The fluoride ion is widely distributed in nature. The main component responsible for its contribution to the diet is water or foods reconstituted with water, such as soup, infant formula and vegetable drinks . The concentration of this ion can increase for various reasons such as human activity (pesticides, water fluoridation, etc.) or natural phenomena (volcanic emissions, soil erosion with high fluoride content, fluoride leaching into water) . In the case of soybean beverages, the reasons for the presence of fluoride are the fluoride content of the soil, the fluoride concentration of the water used in the soybean harvest and the water used in producing the homogenate.
The European Food Safety Authority (EFSA) indicates that it is a non-essential trace element since it is not essential [19,20]. The main route of fluoride absorption is passively through the gastrointestinal tract. The fluoride distribution through the blood facilitates its deposit mainly in the teeth, favoring the formation of fluorapatite and giving greater strength to dental enamel and resistance to acids and inhibiting the metabolism of cariogenic bacteria. Likewise, it increases its hardness in the bones and prevents the appearance of osteoporosis.
However, if fluoride intake is excessive (>10 mg/L day), it is related to dental fluorosis characterized by the appearance of opacity, discoloration of the dental enamel and disfigurement of the teeth. Furthermore, bone fluorosis can occur as a consequence of an increase in bone mass and ossification of cartilage due to alteration of calcium metabolism. In addition, excess is related to metabolic, brain, fertility problems, etc. [21,22,23,24,25]. For this reason, the Institute of Medicine’s Food and Nutrition Board  established acceptable daily intake (ADI) levels based on age and physiological state (Table 1).
Table 1. Fluoride ADI values (estimated daily intake) according to age and physiological state .
Soybean beverages do not have maximum fluoride levels in European or North American legislation; therefore, due to the lack of regulation of the content of this ion, the value established for water for human consumption will be taken as an example, which has a parametric level of 1.5 mg/L of fluoride [27,28]. Likewise, it should be noted that in bottled water, it is mandatory to indicate the level of fluoride .
These data and studies previously published by various authors [30,31,32] indicate that soybean beverages may have a high content of fluoride, favoring dental fluorosis as a consequence of use of water for its manufacture. Thus, the need to determine the fluoride content in marketed soy beverages is established.
The objectives established are (i) to determine the levels of fluoride in soybean beverages of the most popular commercial brands in Spain, (ii) to study the possible statistical differences between the soybean beverages of the different brands analyzed and (iii) to evaluate the toxic risk from fluoride intake as a consequence of the consumption of soybean beverages, considering the values of admissible daily intake (ADI).
The three brands of soybean beverages analyzed have a high concentration of fluoride, especially A-Brand. It should be noted that A-Brand and B-Brand contain sea salt, which can increase the fluoride content in the final product. The consumption of any of these three brands of soybean beverages can pose a health risk in infants and children due to the high amount of fluoride. Intake of up to three servings of soybean beverages in >9 years does not pose a health risk, but considering other dietary sources of fluoride, it may exceed the ADI with consequent health risk. The consumption of one serving is recommended for people over 9 years old. In the case of higher intake, it is advisable to consume the brand with the lowest concentration of fluoride, avoiding consuming more than three servings so as not to exceed the ADI.
The traceability of the raw material and the control of the fluoride content of the different ingredients that these beverages contain is considered as something completely necessary by the food industry. Likewise, considering the importance of vegetable beverages, such as soybean, it is necessary to establish controls over the fluoride content in these products to ensure their quality and safety.