minimal supplies, but will require phlebotomy services/training. Most blood sam-
pling should be done in a fasting state of at least 8 h. Clearance in blood for most
nutrients and bioactives is relatively slow and for the majority of nutrients some
biological pool or storage capacity exists to optimize nutritional status despite
variable daily intake. Urinary samples should be collected relative to the time of
exposure for water-soluble nutrients and bioactives, given that clearance for many
compounds occurs over a relatively short (<8 h) time frame and may demonstrate
peak clearance within an even shorter time frame (2–3 h). Examples are urinary
anthocyanins (the blue/purple pigment in fruits and vegetables) (Kay 2006 ) or tea
polyphenols (micronutrients) (Clifford et al. 2013 ).
Participant Burden
While perhaps not as obvious, the collection of biosamples may cause undue
burden to participants. Phlebotomy associated with blood sampling can be asso-
ciated with pain, bruising, or even tissue damage. Urine collections can be bur-
densome to participants in terms of time, effort, or even comfort level in collection
of urine and subsequent storage. Similarly, stool sampling can be unacceptable to
select individuals. Some samplings such as tissue biopsies may be done under
sedation in order to reduce participant burden; while other biopsies such as adipose
tissue collections from the buttocks may be acceptable and well tolerated by some
individuals but not others. Attention to participant burden and acceptance is an
important aspect of biomarker research and needs to be carefully evaluated in
advance of study.
Nutrient, Bioactive Deposition
Importantly, the biosample should be a valid and reliable source of the nutrient or
bioactive under study. For example, evaluating fatty acids using fat tissue biopsies
is appropriate, but using fat biopsies to study water-soluble nutrients would not be
appropriate. Hair and toenails are appropriate for the assessment of trace elements
wherein depots are minimal and longer term exposure estimates better reflect
nutritional status. Urine and blood both serve as relevant biosample sources for
most water-soluble nutrients. Bile acids and microbiota will require stool and/or
gastrointestinal tissue samples for evaluation while sweat (and sweat pH) may be a
viable biosample source when evaluating sodium excretion during exercise
(Oncescu et al. 2013 ). Other biosample sources include saliva for quantification of
nitrate exposure (Sanchez et al. 2014 ), and exhaled gases have been evaluated in
relation to breath methanol concentrations as an indicator offiber and/or fruit and
vegetable intake in patients with end-stage renal disease (Lee et al. 2012 ).
186 T.E. Crane and C.A. Thomson