Although gamma oryzanol, a compound found in rice bran, has been used in Japan for decades, studies are still uncovering its many potential health benefits. Read on to find out why this supplement is gaining in popularity.
What Is Gamma Oryzanol?
Gamma oryzanol occurs in rice bran oil at a level of 1 to 2%. It comprises a mixture of ferulic acid esters and phytosterols [1, 2].
Apart from rice, it is also found in wheat, maize, rye, triticale, and barley, but at much lower levels [3].
It has been used as a supplement in Japan since the early 70s.
Gamma oryzanol is believed to:
- Lower bad cholesterol. Phytosterols (plant sterols) found in this supplement have a structure similar to cholesterol and are well known for their LDL-cholesterol-lowering effect [4].
- Reduce inflammation [5, 6].
- Lower blood glucose [7].
- Exert antioxidant activity. This is due to ferulic acid, a strong antioxidant that protects cells from reactive oxygen species (ROS) [8, 9].
Gamma oryzanol is commonly used as an exercise supplement as well as to build muscles. However, the results regarding muscle strength are controversial. It is much more promising as a supplement to decrease cholesterol.
Mechanisms of Action
Researchers believe that gamma oryzanol could decrease cholesterol by:
- Decreasing the uptake of cholesterol by gut cells [10].
- Decreasing HMG-CoA reductase activity. HMG-CoA reductase is an enzyme that promotes cholesterol production [10, 11].
- Blocking the formation of micelles, which are small aggregates of molecules that often contain cholesterol [10, 12].
Researchers further believe that this supplement could lower inflammation by:
- Decreasing NF-kB – the master-regulator of inflammation [13].
- Decreasing inflammatory molecules PGE2, COX-2, TNF-alpha, and IL-6 [5, 6].
- Lowering CRP – a marker of chronic low-grade inflammation [14].
Gamma oryzanol also has antioxidant activity in cells [15].
In animals and cells, it lowers blood glucose levels by increasing PPAR-γ and C/EBPα, which increases the uptake of glucose by cells [7].
Potential Benefits of Gamma Oryzanol
Gamma oryzanol supplements have not been approved by the FDA for medical use. Supplements generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
Possibly Effective For
1) Cholesterol
Gamma oryzanol blocks the uptake of cholesterol by gut cells, as it decreases HMG-CoA reductase, an enzyme that promotes cholesterol production. This supplement also increases cholesterol removal by bile acids [10, 16].
In 30 men with high cholesterol, rice bran oil, with varying amounts of gamma oryzanol, was able to lower total and LDL cholesterol levels. However, there was little difference between the cholesterol-lowering effects of the high and low gamma oryzanol-containing rice bran oil [17].
Gamma oryzanol decreased total cholesterol and LDL cholesterol levels in 20 schizophrenia patients with high cholesterol [18].
In another study, this supplement lowered cholesterol and improved fat metabolism in rats fed a high-cholesterol diet [19].
The compound was effective in lowering LDL-cholesterol levels and increasing HDL-cholesterol in rats. Low HDL and high LDL-cholesterol increase the risk of heart disease [20, 21].
Gamma oryzanol decreased cholesterol levels in hamsters with high cholesterol [22].
It also lowered cholesterol absorption by 20% and increased cholesterol removal by bile acids in rats [16].
Insufficient Evidence For
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of gamma oryzanol for any of the below-listed uses. Remember to speak with a doctor before taking gamma oryzanol supplements, and never use it in place of something your doctor recommends or prescribes.
2) Muscle Strength
A study of 30 healthy participants found that gamma oryzanol improved bench press and leg curl results, showing that the supplement may have improved muscle strength during resistance training [23].
However, another study on 22 weight-trained men showed that nine weeks of gamma oryzanol supplementation did not influence performance [24].
Animal Research (Lacking Evidence)
No clinical evidence supports the use of gamma oryzanol for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
3) Atherosclerosis
Rice bran enzymatic extract (containing gamma oryzanol) lowered cholesterol and prevented atherosclerotic plaque development in atherosclerosis-prone mice on a high-fat diet [25, 26].
This compound decreased cholesterol and reduced “aortic fatty streaks” in hamsters. Fatty streaks are the first visible damage in the hardening of the arteries [27].
However, it was ineffective in treating the hardening of the arteries (atherosclerosis) in rabbits [28].
4) Diabetes
Gamma oryzanol improved glucose levels in mice by improving the function and survival of pancreatic beta cells (cells that release insulin) [29].
This compound directly acts on pancreatic cells to enhance glucose-stimulated insulin release [30].
Also, it directly enhances glucose uptake by fat cells (adipocytes) [7].
This supplement effectively prevented the decrease of adiponectin levels in mice. Low adiponectin is a risk factor for diabetes [31].
Gamma oryzanol increased insulin sensitivity in rats with type 2 diabetes [32].
When pregnant mice are fed a high-fat diet, their offspring develop insulin resistance. Gamma oryzanol given to pregnant mice prevented the development of insulin resistance in the offspring [33].
5) Obesity
A study performed on rats suggests that gamma oryzanol can combat obesity by blocking dopamine receptors (D2R) in the brain (striatum). These receptors are part of the brain reward system. They are increased by a high-fat diet, resulting in hedonic overeating [34].
This compound reduced the preference for dietary fats, and reduced obesity and fat accumulation in rats fed a high-fat and high-fructose diet [35, 14].
It also decreased the production of fat cells (adipocytes) [36].
6) Skin Health
When delivered under the skin via an injection, gamma oryzanol protected against skin-aging and improved wrinkles in 15 people and UV radiation-exposed rats [37].
Also, when it was incorporated into a cream and applied to the skin, it hydrated and lightened the skin [38].
7) Osteoporosis
This compound increased bone density and calcium content in a rat model of osteoporosis (female rats that had their ovaries removed) [39].
Another study found that it increased bone formation-related genes in rats (SP7/OSX, POSTN, RUNX2, and COL1 and 2) [40].
8) Inflammation
In rats, gamma oryzanol decreased inflammatory mediators such as PGE2, TNF-alpha, and IL-6 [5].
This supplement reduced lung inflammation in rats with sepsis [41].
It also decreased IL-6 and a marker of chronic low-grade inflammation, CRP, in rats with metabolic syndrome [14].
Gamma oryzanol also decreases other inflammatory parameters, such as COX-2 and Nf-kB [13, 6].
9) Anaphylaxis
Anaphylaxis is an extreme allergic reaction characterized by swelling and difficulty breathing.
A component of gamma oryzanol called cycloartenol ferulate was able to reduce mast cell degranulation (mast cells release histamine and other inflammatory agents), which decreased the anaphylaxis reaction in rats [42].
10) Hair Growth
A rice bran extract containing gamma oryzanol promoted hair growth and the formation of new hair follicles in mice [43].
11) Immune Response
This supplement increased cytokines IL-8 and CCL2 and enhanced the activity of macrophages ( a type of white blood cell) important for the innate immune responses [44].
12) Heavy Metal Toxicity
This compound protected mice against cadmium-induced testicular toxicity and oxidative stress [45].
13) Ulcers
In a couple of studies, gamma oryzanol prevented stress-induced ulcers in rats [46, 47].
Cancer Research
Gamma oryzanol inhibited colon tumor growth in mice, probably by [48]:
- Increasing natural killer (NK) cell activity
- Increasing cytokines TNF-alpha, IL-1beta, and IL-6
- Reducing blood supply to the tumor
Cycloartenol ferulate, a component of gamma oryzanol, reduced the growth of skin tumors in mice [49].
Gamma oryzanol inhibited the growth of human prostate cancer cells [50, 51].
However, a study on rats reported a rare side effect of gamma oryzanol: promoting lung cancer. But its effect is weak and occurs only at a very high dosage [52].
Gamma oryzanol has not been studied in human cancer patients. We strongly recommend against using it without first consulting your doctor.
Limitations and Caveats
Most of the studies on gamma oryzanol have been in animals or cells, which may or may not translate and apply to human health.
Despite the frequent use of gamma oryzanol by athletes as a strength supplement, there is limited evidence available to support the effects of this compound on muscle strength during resistance training [23].
The testosterone-lowering effects of gamma oryzanol are only theoretical and haven’t yet been proven [53].
Further studies are needed to confirm that gamma oryzanol reduces HMG-CoA reductase activity in humans [10].
Gamma Oryzanol and Hormones
Gamma oryzanol did not influence testosterone, cortisol, estradiol, growth hormone, or insulin levels in humans [24].
Another study found that an injection of gamma oryzanol into rats suppressed growth hormone and prolactin release [54].
This compound was a potent inhibitor of luteinizing hormone release and a weak inhibitor of prolactin in rats [55].
It lowered thyroid-stimulating hormone (TSH) levels in 6 of the 8 studied hypothyroid patients the blood [56].
Safety
Gamma oryzanol and its source, rice bran oil, are generally considered to be safe, with little to no side effects reported in studies.
Gamma oryzanol is a promoter of lung cancer in rats, but its effect is weak and occurs only at a very high dosage [52].
It was found to be not carcinogenic (cancer-causing) in studies on experimental mice and rats [57, 58].
Supplementation
Dosage
There is no safe and effective dose of gamma oryzanol for any health purpose because no sufficiently powered study has been conducted to find one. That said, clinical studies have found benefits associated with certain doses.
Some studies used a lower dose of around 50 to 60 mg daily [59, 60].
One study (referenced in a review) administered gamma oryzanol thrice daily at 20 mg [59].
Others used a higher dose, between 300 and 800 mg daily [61, 23].
