This 2-year case study showed that drinking the preparation of N. sativa tea daily increased the occurrence of hypoglycemia and lowered the HbA1c level. As a result, injection of insulin glargine was reduced from 38 units to 25 units and injection of insulin aspart was reduced from 10 units to 5 units, while maintaining almost the same HbA1c level as that at the baseline (7%). Previously, several authors (Bamosa et al. 2010; Hosseini et al. 2013; Kaatabi et al. 2015; Heshmati et al. 2015) also reported that N. sativa seeds, in the form of powder or oil, reduced HbA1c. Unlike the study by Ansari et al. (2017), this case study showed that N. sativa tea can be used to reduce the glucose level in a 72-year-old with type-2 diabetes and stage 3–4 chronic kidney disease.

This study also showed that drinking N. sativa tea daily lowered body weight and thus reduced dosage of furosemide by 4 mg or more. In this case study, further reduction of furosemide dosage was not possible without the supplementation of medication such as empagliflozin (Neeland et al. 2016) because of the 72-year-old’s pulmonary arterial hypertension. This is the first report to demonstrate that N. sativa mitigates edema which was related to congestive heart failure. Decrease in body mass index due to N. sativa seeds was noted by Hosseini et al. (2013) and Heshmati et al. (2015).

Another benefit of N. sativa tea was the desirable change from high triglycerides (3.9 mmol/L) to normal triglycerides level (1.5 mmol/L). High triglycerides increase the risk of stroke, heart attack and heart disease. Tasawar et al. (2011) and Heshmati et al. (2015) also found that N. sativa seeds reduced the triglycerides level. The total cholesterol and HDL cholesterol levels were normal at the baseline. Throughout the course of this study, N. sativa tea brought little change in total cholesterol, HDL cholesterol, and LDL cholesterol levels. Changes in total cholesterol, HDL cholesterol, and LDL cholesterol levels were reported by others (Heshmati et al. 2015; Tasawar et al. 2011). eGFR levels indicate a stage 3 chronic kidney disease (i.e., eGFR is between 30 and 59) and these were relatively stable, but UACR increased over the two years. High UACR, may be alleviated by supplementation of empagliflozin (Cherney et al. 2017).

Nigella sativa oils contain many phytochemicals, including thymoquinone, linoleic acid, oleic acid, palmitic acid, stearic acid, etc., with thymoquinone being a major phytochemical component of the seeds’ volatile oil (14.5%) (Heshmati et al. 2015; AbuKhader 2012). Pure thymoquinone has shown a lowering of the blood glucose level in rats. It has been postulated that the hypoglycemic effect of N. sativa seeds is the result of thymoquinone restoring the activity of enzymes involved in glucose metabolism and/or having a protective effect on β-cells of the pancreas against the damaging effect of oxidative stress and nitric oxide (AbuKhader 2012).

Coincidentally, metformin is derived from galegine, a natural product from the plant Galega officinalis, used in herbal medicine in medieval Europe. It is usually the first-line medication for the treatment of type 2 diabetes. Despite its clinical use for 60 years, its molecular mechanisms of action remain not very clear (Rena et al. 2017).

AAC Starbuck barley seeds contain an average amount of ß-glucan and reasonable levels of total antioxidant phenols and antioxidant capacity (Choo et al. 2015). It has been shown that ß-glucan improves glycemic control in type-2 diabetes (Pick et al.1998). Wheat seeds probably act as a thickening agent for the N. sativa tea.

In conclusion, this 2-year case study showed that drinking N. sativa tea daily lowered the blood glucose level and reduced body weight in a 72-year-old with type-2 diabetes, stage 3 chronic kidney disease, and congestive heart failure, and thereby reduced the dosages of insulin injection and diuretic intake. The cost of the ingredients is low, $4 per 200 gm N. sativa seeds, $0.8 per 200 gm wheat kernels, and $0.8 per 200 gm barley grains (all in Canadian currency). The modest cost and ease of preparation make N. sativa tea very attractive for glycemic and edematous control for people in low- and middle-income countries. N. sativa tea will also be useful as an alternative in high-income countries.