Provided are methods for determining the amount of vitamin C in a sample using mass spectrometry. The methods generally involve ionizing vitamin C in a sample and detecting and quantifying the amount of the ion to determine the amount of vitamin C in the sample.

Provided herein are methods for diagnosing impaired nutrient absorption or determining a nutrient absorption level in an individual. A first stable absorption isotopologue of a nutrient and a second stable absorption isotopologue of the same nutrient are administered orally and intravenously, respectively, to the individual. Amounts of the first and second isotopologues are both measured in blood samples drawn periodically and a ratio of the first isotopologue to the second isotopologue is calculated providing a level of nutrient absorption. The results are compared with a healthy control or an ideal value of 1.0. The ratio less than that of a healthy control or significantly lower than 1.0 indicates an impaired nutrient absorption in the individual.

Provided herein are antigenic molecules that can be used to generate antibodies capable of binding to a vitamin D derivative, such as 25-hydroxyvitamin D2 and/or 25-hydroxyvitamin D3, or a 25-hydroxyvitamin D analog, such as a vitamin D-C22 immunogenic molecule or compound. Antibodies produced using these antigenic molecules, and related antigenic compounds, are also described. In addition, disclosed herein are methods for detecting vitamin D deficiency in a subject, methods for treating a subject suspected of having a vitamin D deficiency, methods for monitoring progression of vitamin D deficiency in a subject, and methods for monitoring treatment of vitamin D deficiency in a subject in need thereof. The methods involve the detection or quantification of 25-hydroxyvitamin D2 and D3. Also provided are methods and reagents for the detection or quantification of 25-hydroxyvitamin D2 and D3, methods for stabilizing vitamin D analogs, and methods for separating 25-hydroxyvitamin D2 and D3 from vitamin D binding protein in a biological sample.

The present invention provides a method of modulating appetite and/or body weight in a subject, said method comprising administering to said subject an effective amount of a MIC-1-modulating agent, wherein said agent increases or decreases the amount of MIC-1 present in said subject, or inhibits or enhances the biological activity of MIC-1 present in said subject.

The present invention discloses novel mechanisms in the aging process and describes novel methods for high-throughput screening to identify, detect, and purify agents to be used for improving mitochondrial function, maintaining the cell cycle-arrested state in senescent and post mitotic cells, and thus preventing or treating age-related diseases or disorders associated with accelerated mitochondrial function loss, telomere dysfunction, and/or deterioration of the growth-arrested state. The present invention also discloses a number of compounds or compositions identified from this method. The present invention further provides the use of low doses of rapamycin or its analogs as a mimic of caloric restriction in preventing age-related diseases or disorders.

Provided herein are antigenic molecules that can be used to generate antibodies capable of binding to a vitamin D derivative, such as 25-hydroxyvitamin D2 and/or 25-hydroxyvitamin D3, or a 25-hydroxyvitamin D analog, such as a vitamin D-C22 immunogenic molecule or compound. Antibodies produced using these antigenic molecules, and related antigenic compounds, are also described. In addition, disclosed herein are methods for detecting vitamin D deficiency in a subject, methods for treating a subject suspected of having a vitamin D deficiency, methods for monitoring progression of vitamin D deficiency in a subject, and methods for monitoring treatment of vitamin D deficiency in a subject in need thereof. The methods involve the detection or quantification of 25-hydroxyvitamin D2 and D3. Also provided are methods and reagents for the detection or quantification of 25-hydroxyvitamin D2 and D3, methods for stabilizing vitamin D analogs, and methods for separating 25-hydroxyvitamin D2 and D3 from vitamin D binding protein in a biological sample.

Provided herein are methods for measuring bioavailability of nutrients in a subject after a meal, modeling nutrient metabolism in a subject in need thereof and monitoring nutrient requirements in a patient. The methods utilize a combination of stable isotope-labeled pulse tracers and compartmental analysis to determine at least bioavailability of amino acids in the meal or intracellular amino acid responses to meal components. Also provided is a profile of nutrient metabolism produced by the methods.

Provided are methods for assessing lysosomal dysfunction, as well as for diagnosing specific lysosomal storage diseases. The methods employ CD63 as a biomarker and can be used for the diagnosis and monitoring of conditions, as well as for the monitoring and/or adjustment of therapeutic interventions for such conditions. Also provided are assays and kits for use in said methods.

Contemplated test kits and methods for food sensitivity are based on rational-based selection of food preparations with established discriminatory p-value. Particularly preferred kits include those with a minimum number of food preparations that have an average discriminatory p-value of 0.07 as determined by their raw p-value or an average discriminatory p-value of 0.10 as determined by FDR multiplicity adjusted p-value. In further contemplated aspects, compositions and methods for food sensitivity are also stratified by gender to further enhance predictive value.

Contemplated test kits and methods for food sensitivity are based on rational-based selection of food preparations with established discriminatory p-value. Particularly preferred kits include those with a minimum number of food preparations that have an average discriminatory p-value of 0.07 as determined by their raw p-value or an average discriminatory p-value of 0.10 as determined by FDR multiplicity adjusted p-value. In further contemplated aspects, compositions and methods for food sensitivity are also stratified by gender to further enhance predictive value.