ABSTRACT
There is growing awareness that carotenoids may have an important role in the
maintenance and promotion of good health and in the prevention of chronic
disease (1). Much of this evidence derives from physiology studies that
investigate carotenoid function in the tissues of interest or from epidemiological
studies that relate various measures of carotenoid levels with disease status. The
physiology studies normally employ quantitative analytical methods such as
organic solvent extraction followed by high-performance liquid chromatography
(HPLC) analysis to determine levels with high sensitivity and specificity, but
they are invasive assessments requiring tissue biopsies or autopsy materials.
Epidemiological studies generally rely on three means of assessment-dietary
histories, serum carotenoid levels, and adipose carotenoid measurements-but
these methodologies have many inherent weaknesses. Dietary assessment is an
inexact science because it either relies on long-term subject recall via food
frequency questionnaires or it employs short-term instruments such as food
intake diaries that may not reflect long-term intake patterns. Recall bias can
severely confound such assessments, and there may be large individual variations
in carotenoid bioavailability. Serum and/or adipose levels of carotenoids are also commonly employed in these studies, but these are by definition invasive
techniques since blood must be drawn or fat biopsies performed. The half-lives
of carotenoids in the serum are measured in days, and in adipose tissues the
half-lives are even longer, so that these levels are probably reasonable measures
of medium-and long-term dietary intake, but they do not necessarily correlate
well with levels in tissues, especially if saturable and specific uptake mechanisms
are utilized. Thus, there has been considerable interest in the development of
noninvasive means of assessment of carotenoid levels in accessible tissues. If
reliable and repeatable, these noninvasive techniques can provide a convenient
means to facilitate epidemiological inquiries on large populations. Likewise,
these methods can prove invaluable in physiological and clinical studies since
they can be used as repeated measures to monitor response to dietary or
supplement interventions. This chapter will review the advantages and weak-
nesses of various noninvasive carotenoid assessment techniques used on the two
most accessible human organs: the eye and the skin.
