One of the top fruits when it comes to the antioxidant lycopene, watermelon racks up even more nutrition points because it’s an excellent source of vitamins A and C. Two cups of watermelon is also a good source of potassium, a key nutrient when it comes to healthy blood pressure.
As the name implies, watermelon is rich in water (about 92%), which is why they feel so heavy when you pick them up. It’s this high water content that makes watermelon a fantastic summer food that nourishes, refreshes and hydrates at the same time. And one cup of diced watermelon has just 46 calories. Savor it as a refreshing snack, in a salad or for dessert.
Cardiology (Cardiovascular Disease)
Watermelon’s red pulpy flesh contains the “mother of all antioxidants,” glutathione, which is known to help strengthen the immune system. It’s also high in vitamins C and A. As if that weren’t enough to convince you to eat more of this superfruit, among fruits and vegetables, watermelon has the highest concentration of lycopene, the powerful antioxidant that helps fight heart disease and cancer.
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Sulfur is an important mineral that occurs naturally in some plant and protein foods.
It’s required for the structure and activity of important proteins and enzymes in the body. Notably, sulfur is required for the synthesis of glutathione (2).
Sulfur is found in two amino acids in food: methionine and cysteine. It’s primarily derived from dietary proteins, such as beef, fish and poultry.
However, there are vegetarian sources of sulfur as well, such as cruciferous vegetables like broccoli, Brussels sprouts, cauliflower, kale, watercress and mustard greens.
Vitamin C is a water-soluble vitamin found in a variety of foods, particularly fruits and vegetables.
Strawberries, citrus fruits, papayas, kiwis and bell peppers are all examples of foods rich in vitamin C.
This vitamin has many functions, including working as an antioxidant to protect cells from oxidative damage. It also maintains the body’s supply of other antioxidants, including glutathione.
Researchers have discovered that vitamin C may help increase glutathione levels by attacking free radicals first, thereby sparing glutathione.
They also found that vitamin C helps reprocess glutathione by converting oxidized glutathione back to its active form (8).
In fact, researchers have found that taking vitamin C supplements increased glutathione levels in white blood cells in healthy adults.
In one study, adults took 500–1,000 mg of vitamin C daily for 13 weeks, leading to an 18% increase of glutathione in white blood cells (8).
Another study showed that taking 500 mg of vitamin C supplements per day increased glutathione in red blood cells by 47% (9).
However, these studies involved vitamin C supplements. Given that supplements are concentrated versions of the vitamin, it’s unclear if foods would have the same effect.
Further research is needed to determine if you can increase glutathione levels by eating foods containing vitamin C.
Selenium is an essential mineral and a glutathione cofactor, meaning it’s a substance needed for glutathione activity.
Some of the best sources of selenium are beef, chicken, fish, organ meats, cottage cheese, brown rice and Brazil nuts.
By increasing your intake of selenium, you may help maintain or increase your body’s supply of glutathione.
The Recommended Dietary Allowance (RDA) for selenium for adults is 55 mcg. This is based on the amount needed to maximize the production of glutathione peroxidase (10).
One study investigated the effects of selenium supplements in 45 adults with chronic kidney disease. All of them received 200 mg of selenium daily for three months.
Interestingly, all of their glutathione peroxidase levels increased significantly (11).
Another study showed that taking selenium supplements increased glutathione peroxidase levels in patients on hemodialysis (12).
Again, the above studies involved supplements, rather than selenium-rich foods.
Additionally, it’s important to note that the tolerable upper intake level (UL) is set at 400 mcg per day. Due to possible toxicity, be sure to discuss selenium supplements and dosage with your healthcare provider.
For most healthy adults, eating a balanced diet with selenium-rich foods will ensure adequate levels of selenium — and, therefore, healthy glutathione levels.
However, dietary glutathione is poorly absorbed by the human body. Additionally, cooking and storage conditions can decrease the amount of glutathione found in food.
Despite having a lower impact on increasing glutathione levels, glutathione-rich foods may help decrease oxidative stress.
For example, a non-experimental study showed that people who consumed the most glutathione-rich foods had a lower risk of developing mouth cancer (14).
Ultimately, further research is warranted to fully understand the effect of glutathione-rich foods on oxidative stress and glutathione levels.
Your body’s production of glutathione depends on certain amino acids.
An amino acid called cysteine is a particularly important amino acid that is involved in glutathione synthesis.
Foods rich in cysteine, such as whey protein, may increase your glutathione supply (15).
Milk thistle supplements are another way to boost glutathione levels naturally.
This herbal supplement is extracted from the milk thistle plant, known as Silybum marianum.
Milk thistle is comprised of three active compounds, collectively known as silymarin. Silymarin is found in high concentrations in milk thistle extract and is well known for its antioxidant properties (20).
Researchers believe that silymarin is able to maintain glutathione levels by preventing cell damage (23).
Turmeric is a vibrant yellow-orange herb and a popular spice in Indian cuisine.
The curcumin content is much more concentrated in the extract form of turmeric, compared to the spice.
Researchers conclude that the curcumin found in turmeric may assist in restoring adequate levels of glutathione and improve the activity of glutathione enzymes.
To experience an increase in glutathione levels, you would need to take turmeric extract, as it would be extremely difficult to consume the same levels of curcumin with turmeric spice.
A good night’s rest is essential for overall health. Interestingly, long-term lack of sleep can cause oxidative stress and even hormone imbalances (29).
Furthermore, research has shown that chronic lack of sleep may decrease glutathione levels.
For example, a study measuring glutathione levels in 30 healthy people and 30 people with insomnia found that glutathione peroxidase activity was significantly lower in those with insomnia (30).
Therefore, making sure you get good, restorative sleep each night may help maintain or boost your levels of this antioxidant.
Regular physical activity has long been recommended by physicians and healthcare providers. It’s no surprise that exercise is good for both your physical and mental health.
Recent research shows that exercise is also helpful in maintaining or increasing antioxidant levels, especially glutathione.
Completing a combination of both cardio and circuit weight training increases glutathione the most, compared to completing cardio or weight training alone (34).
However, athletes who overtrain without maintaining adequate nutrition and rest may be at risk of decreased glutathione production (35).
Therefore, be sure to incorporate physical activity into your regular routine in a gradual and sensible way.
It’s no surprise that many adverse health effects are associated with chronic and excessive alcohol intake.
Alcoholism is commonly associated with ailments such as liver cirrhosis, brain damage and pancreatitis.
While not as well known, lung damage is also an adverse effect of alcoholism. This is likely related to a depletion of glutathione levels in the lungs.
The small airways of the lungs require glutathione to function properly. In fact, healthy lungs have up to 1,000 times more glutathione than other parts of the body (36).
Depletion of glutathione in the lungs of alcoholics is most likely due to oxidative stress caused by chronic alcohol use (37).
Research has identified an 80–90% decrease in lung glutathione levels in those who regularly consume excessive amounts of alcohol (38).
Thus, limiting your alcohol intake may help you maintain healthy glutathione levels.