disease, diabetes, obesity, macular disease). Moreover, the contribution of dietary provitamin A carotenoids to dietary retinol intake
is being questioned based on in vitro and in vivo studies on the
three
major
dietary
provitamin
A
carotenoids
(carotene vs. xanthophyll) [8]; thus, more intervention studies
with specific provitamin A carotenoids from different food matrices
and on subjects with different vitamin A nutritional status should
be conducted as these are crucial aspects affecting bioconversion of
provitamin A carotenoids into retinol.
Intervention studies designed as randomized controlled trials
are the ones considered to provide the most reliable and the strongest evidence in epidemiological research and can generally be
considered either “preventive” (risk reduction of certain chronic
diseases, that is, lutein and zeaxanthin regarding age-related macular degeneration) or therapeutic (effectiveness of provitamin A
carotenoid food sources in preventing or reducing symptoms/
mortality due to a vitamin A deficiency).
In brief, the steps in the development of the intervention study
are as follows: (1) identifying the objective and design of the
intervention study; (2) identifying the target population and define
inclusion/exclusion criteria; (3) selection of biomarkers; (4) selecting sampling method and calculate the sample size; (5) selection of
data collection methods (quantitative and qualitative); (6) taking
out civil liability insurance for research staff involved in the study;
(7) submitting the study protocol, participant information sheet
and the informed consent form to the ethics committee for
approval; (8) recruitment of participants; (9) dietary intervention
(food or isolated compounds), using single-dose (usually for the
assessment of bioavailability, pharmacokinetic and acute effects) or
multiple-dose (medium/long-term trials usually used to evaluate
chronic (cumulative) exposure, functional changes or modification
of risk factors); (10) dietary/nutritional intervention follow-up and
compliance; (11) data analysis and interpretation of results.
2 Materials
2.1 Carotenoid
Sources
The carotenoid material used in the intervention studies can be
foods containing carotenoids (natural or enriched sources), food
supplements or isolated carotenoids at specific doses for a particular
study. The use of stable carotenoid isotopes [9] makes it possible to
differentiate between administered and endogenous carotenoid but
the procedure can be difficult and costly (see Note 2).
2.2 Food
Composition Tables
and Databases
with Carotenoid Data
In general, food composition tables (FCTs) and databases (FCDBs)
did not include carotenoid content and therefore special attention
needs to be paid to those showing the individual content of carotenoids (e.g., refs. [10, 11]). These enable us to properly select the
364
Begon ˜ a Olmedilla-Alonso
is being questioned based on in vitro and in vivo studies on the
three
major
dietary
provitamin
A
carotenoids
(carotene vs. xanthophyll) [8]; thus, more intervention studies
with specific provitamin A carotenoids from different food matrices
and on subjects with different vitamin A nutritional status should
be conducted as these are crucial aspects affecting bioconversion of
provitamin A carotenoids into retinol.
Intervention studies designed as randomized controlled trials
are the ones considered to provide the most reliable and the strongest evidence in epidemiological research and can generally be
considered either “preventive” (risk reduction of certain chronic
diseases, that is, lutein and zeaxanthin regarding age-related macular degeneration) or therapeutic (effectiveness of provitamin A
carotenoid food sources in preventing or reducing symptoms/
mortality due to a vitamin A deficiency).
In brief, the steps in the development of the intervention study
are as follows: (1) identifying the objective and design of the
intervention study; (2) identifying the target population and define
inclusion/exclusion criteria; (3) selection of biomarkers; (4) selecting sampling method and calculate the sample size; (5) selection of
data collection methods (quantitative and qualitative); (6) taking
out civil liability insurance for research staff involved in the study;
(7) submitting the study protocol, participant information sheet
and the informed consent form to the ethics committee for
approval; (8) recruitment of participants; (9) dietary intervention
(food or isolated compounds), using single-dose (usually for the
assessment of bioavailability, pharmacokinetic and acute effects) or
multiple-dose (medium/long-term trials usually used to evaluate
chronic (cumulative) exposure, functional changes or modification
of risk factors); (10) dietary/nutritional intervention follow-up and
compliance; (11) data analysis and interpretation of results.
2 Materials
2.1 Carotenoid
Sources
The carotenoid material used in the intervention studies can be
foods containing carotenoids (natural or enriched sources), food
supplements or isolated carotenoids at specific doses for a particular
study. The use of stable carotenoid isotopes [9] makes it possible to
differentiate between administered and endogenous carotenoid but
the procedure can be difficult and costly (see Note 2).
2.2 Food
Composition Tables
and Databases
with Carotenoid Data
In general, food composition tables (FCTs) and databases (FCDBs)
did not include carotenoid content and therefore special attention
needs to be paid to those showing the individual content of carotenoids (e.g., refs. [10, 11]). These enable us to properly select the
364
Begon ˜ a Olmedilla-Alonso