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A concerning new study published in the European Journal of Nutrition entitled, "Type of sweet flavour carrier affects thyroid axis activity in male rats,” is the first study of its kind to evaluate the effects of sucralose (aka Splenda) on mammalian thyroid function and metabolism. Their findings reveal that sucralose has endocrine disruptive properties on the hypothalamic-pituitary-thyroid axis (HPA axis), resulting in thyroid hormone suppression, increased appetite, and weight gain.
Before we delve into the details of the study, it is important for our readers to understand that this finding is not novel in that there is an accumulating body of research on sucralose showing this chemical marketed as an artificial sweetener is causing a wide range of unintended, adverse health effects. Our sucralose database portal houses the primary study abstracts in one convenient location, and now contains research revealing 15 different signals of harm linked to this artificial sweetener, such as neurotoxicity. Most concerning perhaps is the discovery that sucralose actually produces deadly dioxins when heating. Considering that Splenda is regularly advertised to consumers as a safe sugar alternative specifically for baking applications. For instance, have you seen the TV ads where parents are encouraged to use it presumable to keep their kids healthy? If not, you can visit the Splenda Baking and Cooking page which features a picture of a woman holding her son while baking. As pertains to research relevant to the latest finding, sucralose has already been demonstrating to promote weight gain and diabetes. This removes sucralose's primary marketed ‘benefit.’ Indeed, the new study also found that it promotes weight gain in comparison to sugar. So, let’s get to the study details now:
The straightforward purpose of the study was described as follows:
"Non-nutritive sweeteners are the most widely used food additives worldwide. However, their metabolic outcomes are still a matter of controversy and their effect on the thyroid activity, a key regulator of metabolism, has not been previously studied. Therefore, we aim to determine the influence of the sweet type flavour carrier on selected parameters of thyroid axis activity."
In order to accomplish this, they studied 105 Sprague-Dawley rats, divided into 3 groups, who were fed at their will (ad libitum) for 3 weeks one of the three different diets. The diets had identical caloric content (isocaloric), comprised of starch (wheat starch)differing in the following ways: Diet #1 contained no sugar. Diet #2 contained 10% sucrose (10 grams). Diet #3 contained enough Sucralose (.0167 grams) to create the same sweet flavor intensity as Diet #2 (10% sucrose).
The results were reported as follows:
Results The results obtained indicate that both the presence and the type of sweet taste flavour carrier affect thyroid axis activity both at fasting and postprandial state. Compared to diet with sucrose which stimulates thyroid axis activity, sucralose addition diminishes thyroid hormone synthesis as thyroid peroxidase (TPO) activity, plasma thy- roxine (T4), and triiodothyronine (T3) concentration was lower than in SC and NS while in non-sweet diet the lowest level of hepatic deiodinase type 1 (DIO1) and the highest reverse T3 (rT3) level indicate on altered thyroid hormone peripheral metabolism.
The researchers concluded:
"One principal finding of this study concerns the close relationship between the sweet flavour carrier and the pitu- itary-thyroid axis activity, which is involved in the meta- bolic adaptation to meal composition. This effect may be observed at various levels. Sucralose intake seems to diminish thyroid axis activity by decreasing TPO activity, TSH, and plasma total TH concentrations, but at the same time, it increases both free T3 and T4 indexes. Those find- ings confirmed that sucralose is physiologically active and may provoke disturbances in thyroid axis activity. Aware of uncertainties in the interpretation and extrapolation of data from laboratory animals to humans, we acknowledge that further studies are required to support these findings."
It is important to understand that this study proves sucralose is not metabolically inert as often claimed when questions of its toxicity are raised. Because the researchers used doses of sucralose within the accepted daily average, the implications to humans are undeniable. Sucralose also increased appetite and weight gain — to things that run diametrically opposed to consumer perception and the irresponsible marketing of its “benefits.” The study provides more details:
"Both food intake and body mass gain were signifi- cantly affected by the type of diet (for both p < 0.001). In total, the highest food intake was recorded in the SU group. The average daily intake of sucralose with the diet (14.2 ± 0.4 mg/kg body weight/day) did not exceed the acceptable daily intake (ADI, 15 mg/kg body weight/day).
The food intake recorded during the meal before euthanasia did not differ between NS, SC, and SU, and was 3.98 ± 0.5, 4.22 ± 0.41, and 4.71 ± 0.5, respectively.
The total daily body weight gain in the SU group was significantly higher than in SC and NS, which represented the lowest value (for both p < 0.001). Therefore, the highest diet growth efficiency was also recorded in SU, and there were no differences between NS and SC (Table 2).”
Because previous research has established that carbohydrates affect thyroid axis activity, the study was designed to keep the carbohydrate content identical in order to isolate only the difference between the artificial and natural sweetener.
The question often emerges following animal studies, as to whether the findings can be extrapolated to humans. The study addresses this point directly as follows:
Despite the known species derived differences in thy- roid economy between humans and rodents [65, 66], it was demonstrated that total T4 levels in rodents are a valid indicator of thyroid function in relation to effects in humans . Moreover, humans and rats might be equally sensi-tive to TH synthesis disruptors, and even though in rats the response occurs after a shorter exposure time, the final effect could be the same
Another highly concerning observation was that sucralose’s effects are similar to those observed with other organochlorine chemicals in its class, which include dangerous pesticides.
[T]he pattern of HPT axis compo- nents—decreased TPO activity, TSH, T4, and T3 plasma concentrations together with increased free-to-total TH ratios in the group on the diet with sucralose—resembles some effects evoked by organochlorine compounds docu- mented in human and animal studies. The inverse relation- ships between plasma levels of chloroorganic compounds and TSH or the thyroid hormone have been observed [31–35]. The association between high levels of fT4 and the consumption of fish exposed to organochlorinated xenobiotics was found in adults from a certain area in East Slovakia . This could be explained by the binding of chloroorganic compounds residues to transthyretin . In the light of these parallels, our results could raise questions about the physiological inertness of sucralose.
The stiudy also noted that previous researchers have doubted the safety of sucralose based on observations that sucralose intake alters expression of both “rat intestinal P-glycoprotein (P-gp) and cytochrome P-450 isozymes, which are key components of the detoxi- fication system in first-pass drug metabolism .”
Changes also observed consistent with sucralose as a toxicant are: “Altera- tions in beneficial intestinal microflora and epithelial bor- der function after long-term sucralose ingestion were also recorded [38, 39].”
The researchers confjecture that sucralose’s adverse effects of the thyorid axis would be reflected in “thyroid hisopathology,” i.e. thyroid lesions/tumnors.