Introduction

Diabetes mellitus is a growing problem, particularly type 2 diabetes which used to be termed “late onset” although it is increasingly being seen in younger age groups. This illness is having a large and increasing burden on health care systems around the world including in Aotearoa New Zealand where its incidence in children under 15 years of age has increased by around 5% a year over the last 25 years⁽¹⁾. An estimated 250,000 people in New Zealand now have diabetes, and one in four New Zealanders aged 15 or over have prediabetes, which is where blood glucose levels are higher than normal, but not high enough to be diagnosed as diabetes.  Māori and Pacific populations have around double the prevalence of diabetes than other New Zealanders, and are at least three times more likely to suffer from complications⁽²⁾.

A large percentage of people under the age of 40 years diagnosed with type 2 diabetes are overweight or obese, and so the need to address dietary and lifestyle factors contributing to the development of this disease, is imperative. This can include changes in diet and increased exercise, as well as stress management. Prevention is always preferable to the need to treat a serious chronic illness requiring long term medication.

Medications for type 2 diabetes usually include oral hypoglycaemic drugs such as metformin, and sometimes second line drugs such as empagliflozin which can help reduce renal or cardiovascular complications.  Type 1 diabetes, is treated by intraperitoneal injections of insulin.

Complications of diabetes include a wide range of related symptoms and potential health problems.  It is a major cause of blindness, kidney failure, heart attacks, stroke and amputation of limbs.

While proper diagnosis and management of both Type 1 and Type 2 diabetes is critical and drug medication can be life-saving, dietary changes and appropriately prescribed herbal medicines can also play a useful role. 

Dietary plants

Many plants possess activities of relevance to the prophylaxis or management of Type 2 diabetes and its complications. Epidemiological studies have found diets rich in plant products such as legumes and nuts, berries and vegetables, and the so-called Mediterranean diet, have a lower risk of Type 2 diabetes^(3-5).

Culinary spices such as ginger, turmeric, blackseed and cinnamon, have various actions that may be favourable for diabetic patients. Clinical trials on cinnamon have found it to reduce fasting blood glucose and improve insulin resistance in Type 2 and pre-diabetic patients⁽⁶⁾ . Ginger can reduce elevated levels of inflammatory markers associated with the onset and severity of diabetes^{(7, 8)}. Blackseed (Nigella sativa), a popular culinary space in Mediterranean and many Asian countries, improves the dysfunction seen in the lining (endothelium) of small blood vessels in diabetic patients, as well as kidney, heart and immune functions⁽⁹⁾.

Popular herbal medicines

While these and other plants and spices may help to normalise hyperglycaemia, other objectives in using herbal medicines are more fruitful in diabetic patients. These include the prevention of diabetic complications such as kidney nephropathy, retinopathy, peripheral vascular and cardiovascular disease, and cognitive decline.

One of the common names for the Indian herb Gymnema (Gymnema sylvestre), is ‘Gurmur (or Gudmar)’ in Hindi, which means ‘sugar destroyer’, due to its ability to suppress the sensation of sweetness from eating sweet foods⁽¹⁰⁾. Studies have shown it to reduce blood glucose and elevated cholesterol and triglyceride levels⁽¹¹⁾, and to enhance insulin producing cells in the pancreas in animals^{(11, 12)}.  However claims that its sugar neutralising properties lead to less desire for sweet foods, have not been substantiated⁽¹³⁾.

Other prominent medicinal plants used for diabetes include fenugreek (Trigonella foenum-graecum), bitter melon (Momordica charantia), and turmeric (Curcuma longa).  As with cinnamon, all exhibit a broad range of antioxidant, anti-inflammatory, insulin sensitising or other actions relevant to the development or progression of diabetes and its complications. While some clinical trials have taken place, more large well designed trials and over longer periods of time, are needed.

Prevention of neuropathies and cardiovascular complications

Diabetic nephropathy (deterioration in kidney function) is a serious complication of diabetes, and affects around 30-40% of diabetic patients. It is the leading cause of middle and end-stage chronic kidney disease and accounts for more than 50% of patients entering dialysis or transplant programmes. Like diabetic retinopathy (deterioration in eyesight) it is a serious and debilitating complication of poorly controlled diabetes, and treatment options are expensive and limited.

Many herbal medicines exhibit protective actions against nerve damage and show potential to help prevent such neuropathies.  A recent analysis revealed multiple potentially relevant mechanisms of action for a combination of the Chinese herbs astragalus and dong quai, including inhibition of inflammatory reactions, oxidative stress, glycogen depositions and collagen fibre formation, reduced urinary protein leakages, and improvement in kidney function and other damage caused by high glucose⁽¹⁴⁾.

A number of other neuroprotective and cardioprotective herbal medicines such as green tea, ginkgo, ginseng, withania and rehmannia, may also reduce the risks of diabetic complications such as nephropathy or at least reduce its impact on patients’ lives.

Cardiovascular disease is the leading cause of mortality in people with Type 2 diabetes, and most patients have high blood pressure and an increased risk of heart attack and stroke.  Vascular complications can also lead to claudication and complete peripheral vessel obstruction, resulting in difficult to treat leg ulcers and issues with mobility.

A recent review of 15 randomized controlled trials involving ginkgo as an adjunctive treatment for ischaemic stroke, concluded that it appears to improve neurological function and dependence, at different stages following an ischaemic stroke⁽¹⁵⁾.

A large epidemiological study involving more than 500,000 Chinese adults, recently associated daily green tea consumption with a lower risk of type 2 diabetes and a lower risk of all-cause mortality in patients with existing diabetes. Associations were also made with a lower risk of some diabetic complications⁽¹⁶⁾.

Two common so-called ‘weeds’ which are endemic in our country and which Ive written about previously⁽¹⁷⁾, Japanese honeysuckle (Lonicera japonica) and Chinese privet (Ligustrum lucidum), also possess pharmacological activities of value in the management of diabetes mellitus. Japanese honeysuckle reduces diabetic nephropathy when given to rats, reversing the reduced creatinine clearance, increased blood urea and proteinuria seen when the kidneys are struggling⁽¹⁸⁾. Improvement in diabetic retinopathy, has also been reported in mice⁽¹⁹⁾. Chinese Privet (Ligustrum lucidum), contains flavonoid compounds shown to protect against diabetes-induced osteoporosis in mice⁽²⁰⁾. This is of interest given the frequent coexistence of osteoporosis and increased fracture risk in diabetic patients⁽²¹⁾.

Cognitive decline

The risk of dementia, Alzheimer’s disease, and cognitive decline is higher in people with poor blood sugar control and insulin resistance.  Reduced glucose utilization and deficient energy metabolism also occur early in the course of many patients with Alzheimers’ disease⁽²²⁾.

In addition to improving blood sugar control, plant medicines with the potential ability to reduce nerve cell inflammation within the brain, may provide some benefits in diabetic patients showing signs of cognitive decline. Apart from ginkgo, these include ginseng, blackseed, bacopa, gotu kola, dan shen, lions mane, rosemary and sage.

Diabetic Leg Ulcers

These are common, debilitating and serious complications for diabetic patients. Most don’t heal in a timely fashion and non-healing is associated with complications including infections and sometimes a need for amputation.

While advances have occurred in standard care, more research is critical to identify new and better therapies, particularly given antibiotic resistance and the burden that slow healing ulcers place on the patient and the health care system. Several herbal treatments can be helpful, such as echinacea and horsechestnut, and topical applications such as active manuka honey, which may shorten healing times and lessen the need for antibiotics and hospitalization.

Summary

Diabetes mellitus is a serious and increasingly common condition, and there is a great deal of evidence that plant medicines can help from both preventative as well as management perspectives, particularly with many of its associated complications. However, it is important to also ensure such interventions or adjunctive herbal treatments are prescribed for the particular individual patient, and that the potential for both useful or unwanted interactions with other medications, is taken into account.

While more clinical trials are needed, given the many impacts this illness can have on patients, families and the health care system, even small gains through herbal interventions seem warranted.  These factors and the evidence to date, provides a strong and growing case for more research into specific plants and clinical outcomes.

References:

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