Researchers have recently found that lutein, a compound found in egg yolk, can reduce inflammation levels among patients with heart disease.
In a report on their work in the journal Atherosclerosis, the researchers - from Linköping University (LiU) in Sweden - also describe how they discovered that certain immune system cells take up and store lutein.
Heart disease is a general term for several types of heart condition. The most common form in the United States is coronary artery disease, a condition that restricts blood flow to the heart and causes heart attacks.
Heart disease is the primary cause of death worldwide, with an estimated 17.3 million people dying from the disease every year. This figure is expected to rise to 23.6 million by 2030.
Heart disease is also the number one cause of death in the U.S., responsible for 610,000, or 1 in 4, deaths every year. Of these, 370,000 are down to coronary artery disease.
Having a heart attack is often the first sign for many people that they have coronary artery disease. In the U.S., around 735,000 people experience heart attacks each year.
Atherosclerosis and inflammation
Coronary artery disease develops because a process called atherosclerosis builds up fatty deposits, or plaque, in the walls of the arteries that supply blood to the heart. This results in narrowing arteries that can partially or totally block the flow of blood.
Over time, as the plaque builds up and the arteries become narrower, the heart muscle does not get enough blood. This can cause angina, which is a condition felt as pain or discomfort in the chest and the most common symptom of coronary artery disease.
Coronary artery disease can also lead to heart failure, a condition wherein the heart cannot pump enough blood to meet the body's needs. Other problems, such as irregular heartbeat, or arrhythmia, can also develop.
Advances in basic science have shown that atherosclerosis is not just a fat-depositing process; it also involves an ongoing inflammatory response that plays a key role in all stages of the disease.
The LiU researchers remark that inflammation plays an important role in many aspects of coronary artery disease, such as heart attack and angina.
Study leader Lena Jonasson, who is a cardiology consultant and LiU professor in medical and health sciences, says, "We know that chronic inflammation is associated with a poorer prognosis."
She explains that a significant number of patients who have had a heart attack continue to have persistent low-level inflammation in their bodies, even after effective treatments that involve drugs, revascularization, and lifestyle changes.
Carotenoids and inflammation
In their study paper, Prof. Jonasson and colleagues refer to previous studies that have suggested that what we eat can affect inflammation in our bodies. They highlight a group of compounds called carotenoids, which are "antioxidants with potential anti-inflammatory properties."
Carotenoids are a large family of fat-soluble pigments - that is, compounds that give color to other materials - that are naturally present in vegetables and some animal foods.
The family includes some well-known pigments such as beta-carotene and lycopene. Foods that are rich in lutein - the carotenoid at the center of the new study - include dark green leafy vegetables such as spinach, parsley, and kale. Lutein is also present in egg yolk.
Several studies have found that low levels of carotenoids are linked to higher levels of inflammation markers in the blood. Prof. Jonasson and colleagues wanted to investigate this further, to address the question of whether or not carotenoids themselves possess anti-inflammatory effects.
Some studies have already investigated the relationship between carotenoids and inflammation, but these have either been done in animals or in healthy humans. Their findings, the researchers note, may not have been representative of what happens in the bodies of people with low-level inflammation, such as patients with coronary artery disease, in whom the immune cells are more susceptible to stimulation.
Higher lutein tied to lower inflammation
Thus, for their new study, the LiU team started by investigating the relationship between carotenoids and inflammation in 193 patients with coronary artery disease.
They measured blood levels of six of the most common carotenoids and compared them with blood levels of an inflammation marker known as interleukin-6 (IL-6).
However, the results showed that lutein was the only carotenoid that showed an association with levels of IL-6: "the higher the level of lutein in the blood, the lower the level of IL-6."
Prof. Jonasson comments, "The patients were receiving the best possible treatment for their disease according to clinical guidelines, but even so, many of them had a persistent inflammation. At the same time, the patients had lower levels of lutein."
The team then explored what might be happening at the cell level to produce this effect. After studying immune cells isolated from the blood of patients with coronary artery disease, they found that treatment with lutein reduced the cells' inflammation activity. The carotenoid reduced the cells' production and release of inflammatory cytokines, which are signaling molecules that promote inflammation.
The LiU team now plans to find out whether eating more foods rich in lutein can reduce inflammation in coronary artery disease patients.
"Our study confirms that one particular carotenoid, lutein, can suppress long-term inflammation in patients with coronary artery disease. We have also shown that lutein is absorbed and stored by the cells of the immune system in the blood."
First author Dr. Rosanna Chung, Linköping University, Sweden