What are citrus limonoids used for?

Citrus limonoids are a group of compounds found in citrus fruits that have been extensively researched for their wide range of potential health benefits. Some of the main uses and proposed benefits of citrus limonoids include:

Cancer Prevention

A number of studies have shown that citrus limonoids may help prevent certain types of cancer. Here are some of the main findings:

• Lab studies show citrus limonoids can inhibit growth and promote apoptosis (programmed cell death) in breast, colon, lung, skin, stomach, and mouth cancer cells (1, 2).
• Citrus limonoids blocked tumor formation in animal models of skin, breast, and colon cancer (3, 4).
• Population studies have found higher citrus consumption is associated with lower risk of stomach, breast, and lung cancer (5, 6).
• Proposed mechanisms include inhibiting cell growth signaling pathways, blocking the development of new blood vessels to tumors (angiogenesis), and increasing carcinogen detoxification (7).

While results from lab and animal studies are promising, more research is needed to confirm if citrus limonoid supplementation can help prevent cancer in humans.

Supporting Heart Health

Emerging research suggests citrus limonoids may benefit heart health in several ways:

• They can lower cholesterol levels – studies show citrus limonoids block absorption of dietary cholesterol and increase its excretion (8, 9).
• May lower triglycerides – citrus limonoids reduced triglycerides in animal studies by up to 50% (10).
• Reduce inflammation – citrus limonoids demonstrate anti-inflammatory activities which may benefit heart disease (11).
• Improve arterial function – citrus limonoids improved relaxation of arteries in animal models which may lower blood pressure (12).

More research is required to confirm the cardiovascular benefits of citrus limonoids in humans.

Antimicrobial Effects

Citrus limonoids have been shown to inhibit the growth of various bacteria, fungi, and parasites. Key research findings include:

• Strong antibacterial effects against foodborne pathogens like Salmonella and Listeria (13).
• Antifungal activities against Candida, Aspergillus and dermatophytes (14, 15).
• Anti-parasitic effects against protozoa like Plasmodium and Trypanosoma parasites (16, 17).

The antimicrobial effects of citrus limonoids suggest they could potentially be used as natural food preservatives and anti-infective agents. However further studies are needed to evaluate their efficacy and safety for these applications.

Immune Support

Some research indicates citrus limonoids may enhance immune function. Proposed mechanisms include:

• Increasing white blood cell activity and antibody production (18).
• Enhancing the activity of immune cells like lymphocytes and macrophages (19).
• Modulating pro-inflammatory signaling pathways involved in chronic inflammation (20).

More research is required to confirm whether citrus limonoid supplementation can boost immunity or help treat inflammatory disorders.

Antioxidant Effects

Citrus limonoids demonstrate antioxidant activities in lab studies. Their proposed mechanisms include:

• Scavenging reactive oxygen species and inhibiting lipid peroxidation (21).
• Inducing antioxidant enzymes like superoxide dismutase, catalase and glutathione peroxidase (22).
• Chelating pro-oxidant transition metals like iron (23).

This antioxidant activity suggests citrus limonoids may help protect cells against oxidative damage. However, human data is lacking and more research is required.

Neuroprotective Potential

Some animal studies indicate citrus limonoids may help protect the brain and nervous system. Observed effects include:

• Reduced neuroinflammation and oxidative damage in models of age-related memory loss (24).
• Neuroprotective effects in cell models of Parkinson’s disease (25).
• Improved learning and memory in aged mice (26).

While results from animal studies are promising, human studies are needed to confirm whether citrus limonoids can help preserve cognitive function.

Anti-Diabetic Effects

Early research in diabetic mice found evidence that citrus limonoids may help regulate blood sugar levels. Specific findings include:

• Lowered fasting blood glucose and improved glucose tolerance (27).
• Increased insulin sensitivity and insulin signaling (28).
• Protected pancreatic beta cells, which produce insulin (29).

However, human studies are lacking. More research is needed to verify anti-diabetic effects in people with diabetes.

Kidney Protective Benefits

Some studies suggest citrus limonoids may help protect the kidneys. Proposed mechanisms include:

• Reducing kidney inflammation and oxidative stress (30).
• Preventing drug-induced kidney damage in animal models (31).
• Blocking calcium oxalate kidney stone formation in rats (32).

Additional research is required to confirm the kidney protective effects of citrus limonoids.

Anti-Inflammatory Properties

Citrus limonoids demonstrate anti-inflammatory activities that may benefit a range of inflammatory disorders. Their mechanisms include:

• Inhibiting inflammatory enzymes like cyclooxygenase (COX) and lipoxygenase (LOX) (33).
• Suppressing pro-inflammatory cytokines like TNF-alpha, interleukin-6 and interleukin-1beta (34).
• Blocking NF-kappaB and MAPK inflammatory signaling pathways (35).

Human studies are needed to verify if citrus limonoids can help treat inflammatory conditions.

Detoxification Support

Research shows citrus limonoids can stimulate detoxification enzymes in the liver, intestines and other tissues. Specific effects include:

• Inducing Phase I enzymes like cytochrome P450s which metabolize toxins (36).
• Inducing Phase II enzymes like glutathione S-transferases which conjugate toxins (37).
• Increasing toxin elimination through bile acid secretion (38).

By enhancing detoxification, citrus limonoids may help protect against toxins and environmental pollutants. However, human studies are limited.

Skin Health Benefits

Some studies suggest citrus limonoids may benefit skin health and appearance. Observed effects include:

• Reduced UV damage and wrinkle formation in human skin cells (39).
• Increased hydration and collagen production in human skin cells (40).
• Anti-inflammatory and antioxidant effects to protect skin (41).

Topical products containing citrus limonoids are available, but more research is needed on their efficacy and long-term benefits for skin.

Weight Loss Potential

Some emerging research suggests citrus limonoids may aid weight loss. Proposed mechanisms include:

• Suppresses adipogenesis (formation of new fat cells) (42).
• Reduces fat formation and lipid accumulation in fat cells (43).
• Modulates appetite hormones like leptin to reduce food intake (44).

While results from animal studies are promising, there is no good evidence that citrus limonoids boost weight loss in humans currently.

Conclusion

In summary, citrus limonoids are a unique group of natural compounds found in citrus fruits that have been extensively researched for a wide range of health benefits. The most well-studied benefits with the most promising evidence include cancer prevention, supporting heart health, antimicrobial effects, and immune support. Citrus limonoids demonstrate significant promise in animal and lab studies for numerous other applications ranging from neuroprotection to skin care. However, more high-quality human research is still needed to confirm many of the proposed benefits. Given their generally recognized safety and wide range of biological activities, citrus limonoids have substantial potential as therapeutics and functional food ingredients that may benefit human health.