While we are frequently warned about the perils of cholesterol, there exists quite a bit of evidence which links higher cholesterol levels with improved health outcomes and/or longevity in the elderly. These studies do not prove that cholesterol is conferringbenefit here (only that higher cholesterol is associated with improved outcomes). Nevertheless, it’s perhaps worth at least considering any truly protective role cholesterol may have.
One potentially fruitful avenue concerns the role of cholesterol in immunity. Toxins made by bacteria have been shown to bind to cholesterol, which effectively inactivates them. In one study, mice with genetically high LDL-cholesterol were found to be significantly less prone to death after injection with bacteria compared to mice with lower cholesterol levels [1].
A study out this week adds some support for the idea that cholesterol plays a positive role in immunity. In this study, the relationship between cholesterol levels and outcomes in individuals critically ill with an infection was assessed [2]. Overall, those who died had significantly lower levels of cholesterol compared to those who survived. Again, this sort of evidence does not provide the cholesterol confers benefit. However, it does at least support the idea that cholesterol might have some genuinely protective role.
Another recent study found similar results in individuals undergoing cardiac surgery [3]. Basically, what this research showed was that the higher someone’s cholesterol was, the lower their risk of succumbing to an infection after surgery. For those with the lowest cholesterol levels, rate of infection approached 20 per cent. For those with the highest cholesterol levels, rate of infection was zero.
Another interesting study assessed the potential role of cholesterol in immunity in humans [4]. This study took 21 individuals who had confirmed infection with tuberculosis (TB). All of the individuals were treated with standard TB medication (four antibiotics taken in combination) over a period of 8 weeks.
Of the 21 participants, 10 were given a cholesterol-rich diet (800 mg of cholesterol a day – about the amount of cholesterol found in 5 medium-sized eggs). The rest of the study participants were to eat a diet containing just 250 mg of cholesterol each day.
After two weeks of treatment, 80 per cent of those eating a high-cholesterol diet were free of TB infection, compared to only 9 per cent of the others. This difference was statistically significant. It should be borne in mind that the benefits from the diet may not have come from additional dietary cholesterol per se. The cholesterol came via enrichment of the diet with foods such as butter, beef liver and egg yolk. It’s possible, therefore, that the benefits came from other nutritional elements found in these foods, say. The authors of this study acknowledge this possibility.
Overall, though, the evidence does seem to point to cholesterol conferring benefits for immunity. This may go some way to helping explain the link between higher cholesterol levels and improved longevity in later life.
References:
1. Netera MG, et al. Low-density lipoprotein receptor-deficient mice are protected against lethal endotoxemia and severe Gram-negative infections. J Clin Invest 1996;97:1366–72.
2. Biller K, et al. Cholesterol Rather Than PCT or CRP Predicts Mortality in Patients With Infection. POST ACCEPTANCE, 10 April 2014
3. Lagrost L, et al. Low preoperative cholesterol level is a risk factor of sepsis and poor clinical outcome in patients undergoing cardiac surgery with cardiopulmonary bypass.
Crit Care Med. 2014;42(5):1065-73.
4. Perez-Guzman C, et al. A Cholesterol-Rich Diet Accelerates Bacteriologic Sterilization in Pulmonary Tuberculosis. Chest 2005;127(2):643-51
