Eggs and eyes
Age-related
macular degeneration (AMD) is the leading cause of blindness in the developed
world. In the USA 200,000 new cases are diagnosed each year, and nearly six
million Americans have suffered some vision loss from AMD. A rapidly aging and
longer living population suggests that the prevalence of AMD is likely to
triple over the next 25 years as our populations contain increasing numbers of
older people.
Age
is the biggest risk factor, but diets low in antioxidants low in substances
like lutein and zeaxanthin may also contribute to both low serum and retinal
levels of these antioxidants (Bandolier 123). Higher serum levels are
associated with lower incidence of AMD, as are diets high in antioxidants.
Spinach and other green and yellow vegetables, as well as egg yolk, have high
contents of lutein and zeaxanthin. Recently there has been something of an
interest in eggs, so Bandolier has done a quick review.
Egg evidence
Table
1 contains information from six comparative studies of egg supplementation to
diets. Most of these were randomised, and most examined dietary supplementation
with one egg per day, measuring serum or plasma concentrations of lutein and
zeaxanthin, as well as plasma cholesterol subfractions.
Table 1: Summary of six trials examining dietary egg and changes to serum lutein and/or zeaxanthin concentrations
| Reference | Study | Results |
| Handelman et al. American Journal of Clinical Nutrition 1999 70: 247-251 | Uncontrolled study of 11 subjects aged 48-78 years,
mean LDL cholesterol 4.3 mmol/L Two diets for 4.5 weeks separated by 2 weeks, with or without supplementation with 1.3 egg yolks daily |
Significant increases in plasma lutein and zeaxanthin increased plasma lutein by 28% and 50%, and zeaxanthin by 142% and 114% |
| Surai et al. European Journal of Clinical Nutrition 2000 54: 298-305. | Randomised, double blind, placebo controlled study
in 44 healthy adults aged 26 to 59 years, mean total cholesterol 5.4 mmol/L,
HDL cholesterol 1.2 mmol/L Diets were either commercial eggs or "designer" eggs from chickens fed supplemented diet rich in lutein (15x greater lutein content); one egg per day for 8 weeks |
No increase in plasma lutein with standard egg, but
100% increase with supplemented egg No significant change in total cholesterol or HDL cholesterol |
| Chung et al. Journal of Nutrition 2004 134: 1887-1893. | Randomised, open, comparison of four lutein diets in
10 healthy men aged 26 to 75 years, all with total cholesterol below 6.2
mmol/L Four diets tested, lutein and lutein ester supplement, spinach, and egg yolk, each with 6 mg lutein daily for 10 days |
Serum lutein increased with all diets: lutein 82% lutein ester 83% spinach 141% egg 323% |
| Goodrow et al. Journal of Nutrition 2006 136: 2519-2542. | Randomised, open, comparison of two diets in 33
older individuals, mean age 78 years, mean LDL cholesterol 3.1 mmol/L, total
cholesterol 5.1 mmol/L Diet periods consisted of no eggs and 1 egg daily for 5 weeks |
Serum lutein and zeaxanthin increased by 26% and 38%
on 1 egg per day compared with no egg No change in cholesterol in total or subfractions |
| Wenzel et al. Journal of Nutrition 2006 136: 2568-2573. | Open comparison of placebo pill with diets of
standard and high lutein eggs for 12 weeks in 24 women aged 24 to 59 years
(randomisation not stated). Initial mean LDL cholesterol 2.6 mmol/L, total
cholesterol 4.7 mmol/L |
Change in lutein: placebo -10% ordinary egg +23% high lutein egg +26% Change in zeaxanthin placebo -15% ordinary egg +30% high lutein egg +60% Significant increase in macular pigment optical density with both egg groups No change in serum triglyceride subfractions |
| Herron et al. Journal of Nutrition 2006 136: 1161-1165. | Randomised comparison of 91 people, mean age 31
years, mean total cholesterol 4.3 mmol/L. Analysis according to genetic
subtypes Comparison of 3 eggs daily versus placebo, for 30 days |
In 40 patients in whom they were measured, serum lutein increased by about 30% and zeaxanthin by 20% |
Most
studies showed that eating about one egg a day increased serum or plasma lutein
by about 20-30%. Only one [1] failed to show any increase in plasma lutein with
a standard egg, though it showed a large increase with a “designer”
egg from chickens fed a supplemented diet, with 15 times more lutein per egg
(1.9 mg) than a standard egg.
Two
other results are interesting. One of them [2] compared four diets containing
the same amount (6 mg) of daily lutein as a lutein supplement, lutein ester
supplement, in spinach, or egg. While the study was small, involving only 10
healthy men in the crossover study, it showed a much higher increase in serum
lutein for eggs compared with spinach or supplements for the same daily lutein
dose (Figure 1).
Figure 1: Change in serum lutein concentrations in 10 healthy men with different sources of dietary lutein
Only
one study has examined the effects of dietary eggs on the retina [3].
Individuals with low macular pigment optical density may be at greater risk of
retinal disease because more potentially harmful short wavelength light reaches
tissue at the back of the retina. Higher macular pigment optical density is
considered, therefore, to be protective. In 24 healthy younger women given
placebo or one of two egg diets for 12 weeks, the change in macular pigment
optical density was greatest in those with low initial levels (Figure 2).
Figure 2: Change in macular pigment optical density in 24 women over 12 weeks according to baseline value
Comment
Before
anyone rushes off to stuff themselves with eggs, it needs to be said that these
are early days, though many Internet sites would try and convince readers
otherwise. There is no evidence that eggs are a miracle for preventing or
curing macular degeneration. What we are seeing is a reasonably consistent
response for useful surrogate markers (serum concentrations of lutein and
zeaxanthin or macular pigment optical density), without any major change in
serum cholesterol or its subfractions.
What
is interesting is that lutein in eggs seems to be more readily available, and
that any protective effects are likely to be greatest in those with the
greatest risk, in this case those with the lowest macular pigment optical
density. A good diet, which includes all those leafy greens and some eggs, is
still the right advice, for macular degeneration and all sorts of other ills [4].
References:
- PF Surai et al. Designer egg evaluation in a controlled trial. European Journal of Clinical Nutrition 2000 54: 298-305.
- HY Chung et al. Lutein bioavailability is higher from lutein-enriched eggs than from supplements and spinach in men. Journal of Nutrition 2004 134: 1887-1893.
- AJ Wenzel et al. A 12-wk egg intervention increases serum zeaxanthin and macular pigment optical density in women. Journal of Nutrition 2006 136: 2568-2573.
- JD Ribaya-Mercado, JS Blumberg. Lutein and zeaxanthin and their potential roles in disease prevention. Journal of the American College of Nutrition 2004 23: 567S-587S.