In the United States, people are living longer, healthier lives. Dietary requirements for the elderly must take into account the physiologic changes that occur with aging as these needs differ from those of younger adults. Nutritional support in the elderly is often a primary therapy and it has been shown that those that have an adequate intake of fatty acids and cholesterol as well as a greater intake of vitamins demonstrate higher intellectual function than those who have a deficient diet [1–3].
The habitual consumption of eggs has been shown to provide many nutritional benefits such as higher daily intakes of vitamins C, E and B12, in addition to folate . Deficiencies in these vitamins have been associated with increased risk of cancer, cardiovascular disease and Alzheimer's disease [5–7]. Therefore, the addition of eggs to the diet could actually prevent disease development, particularly in this age demographic who are at elevated risks for the onset of chronic diseases. Additionally, current research has shown that eggs supply a significant amount of the carotenoids lutein and zeaxanthin, which have been linked to the prevention of age-related macular degeneration [8–11], the most common cause of blindness in those over the age of 60. On average, each egg yolk contains 292 μg of lutein and 213 μg of zeaxanthin, along with 0.7 mg vitamin E, 0.5 mcg vitamin B12, and 23.5 mcg folate, all in a highly bioavailable food matrix [12, 13].
Because of the nutrient density of eggs, they are valuable contributors to overall nutritional balance, but they are also a source of dietary cholesterol. Currently, the relationship between plasma cholesterol and dietary cholesterol remains unclear. High serum cholesterol levels have been linked to increased coronary heart disease (CHD) [14, 15] yet the risk of cardiovascular disease in men and women does not increase with increasing egg consumption [16–18] despite their high cholesterol content. Summarizing 166 cholesterol feeding studies conducted over 40 years on 3,500 subjects, a 100 mg/d increase in dietary cholesterol will raise total cholesterol 2.2 mg/dL or about 1% in normal responders . This response relates to a 1.9 mg/dL change in low density lipoprotein (LDL) cholesterol and a 0.4 mg/dL increase in high density lipoprotein (HDL) cholesterol, utimately having little effect on the LDL/HDL cholesterol ratio, and minimal impact on CHD risk . There is a large variation in response however, and hyper-responders are classified as those whose total cholesterol concentration will increase >2.2 mg/dL, and hypo-responders are those for whom total cholesterol increases < 2.0 mg/dL, for every 100 mg/d of dietary cholesterol consumed . This heterogeneity in response confounds the relationship between dietary cholesterol and plasma cholesterol.
Plasma lipoproteins are comprised of a group of diverse particles with various physiochemical characteristics that define each subclass. It is the physiochemical characteristics that determine the degree of atherogenicity of the lipoprotein particle. In clinical practice, it is the cholesterol concentration carried in lipoproteins that captures the attention of the physician. This is the premise behind the use of the LDL and HDL cholesterol concentration ratio as an assessment of CHD risk. However, the evaluation of size deviation among lipoprotein subclasses has shown that normocholesterolemic individuals with a higher concentration of the small, dense LDL particle are at increased risk for coronary heart disease [22–24], despite similar LDL cholesterol concentrations. Similarly, when analyzing the cholesterol concentration of the HDL particle, the protective effects are often amplified when there is a higher concentration the larger subclass (HDL2) which is more antiatherogenic than the smaller HDL3 particle [25–28]. It has been documented that a dietary cholesterol challenge does not impact the LDL/HDL ratio in premenopausal women , or in an elderly population  comprised of both genders. In addition, traditional gel electrophoretic analysis of LDL particle size revealed that the larger LDL particle was predominant in hyper-responders during a dietary cholesterol intervention . It can be surmised then that the cholesterol concentration that each subclass contains can vary by particle size, number, and density. Traditional lipoprotein cholesterol measurements, specifically the LDL/HDL ratio, fail to consider the variability in size distribution. This high degree of variability may therefore lead to inaccurate assessment of CHD risk.
The Adult Treatment Panel III recently acknowledged that the predominance of small dense LDL particles (sdLDL) is an emerging cardiovascular risk factor [32, 33]. It has been reported that LDL size was the best predictor of coronary artery disease [34, 35] and the increase in cardiovascular risk, attributable to lipid factors, was significantly modulated by variations in LDL particle size [32, 36]. Utilizing nuclear magnetic resonance (NMR) spectroscopy, Blake, et al  found that median baseline values of LDL particle concentration were higher and LDL particle size was lower among women who subsequently experienced a coronary event. These evaluations suggest that the measurement of LDL cholesterol content alone is an inadequate marker of CHD risk in the general population. In a cohort of men from the Quebec Cardiovascular Study, the association between LDL particle size and the incidence of ischemic heart disease yielded similar results. In this study, multivariate analysis indicated that sdLDL particles predicted the rate of ischemic heart disease independent of LDL cholesterol content and other lipid risk factors . This large scale, prospective evidence supports a hypothesis that LDL particle size is an important characteristic associated with CHD and that including LDL diameter analysis in CHD risk assessment may increase the accuracy of the evaluation over traditional lipid values.
Carotenoids and cholesterol share common pathways in absorption and transport in the plasma compartment as well as response differences. It is this commonality that led to this study, whose objectives are to evaluate the changes in lipoprotein size, cholesterol content and carotenoid concentration in an elderly population following egg consumption and relate those changes to their impact on CHD risk assessment.