The Tryptophan Requirement in Healthy Adults

The Tryptophan Requirement in Healthy Adults Over 60 Years

The aging population is growing rapidly. For the first time ever, Canadian seniors outnumbered young adults in 2016. Aging is associated with many physical and metabolic deteriorations including the loss of muscle mass and strength, insulin resistance, increased inflammation and oxidative stress.

The muscles of our bodies are composed of proteins and proteins are made of small building blocks called amino acids. Our bodies have the ability to make some amino acids which are called the non-essential amino acids. However, there are certain amino acids that our body's need to make protein but can only be supplied from the foods that we consume. These are called essential amino acids. Tryptophan is one of the essential amino acids that the body needs. Tryptophan is required for protein synthesis and acts as a precursor for serotonin and nicotinic acid. Therefore, there may be a need for more threonine in the diet of older adults. However, the current requirement for threonine is based on studies conducted exclusively in young adults. Thus, the purpose of this study is to find out how much tryptophan older adults need.

Study Overview

• Status: Recruiting
• Conditions: Healthy Aging
• Intervention / Treatment: Other: Tryptophan

Detailed Description

Tryptophan is an essential amino acid and must be obtained from the diet. It is required for protein synthesis and acts as a precursor for serotonin and nicotinic acid. It is of particular importance in the diet of people who receive a large percentage of their calories from cereal grains such as maize, as it is limiting in tryptophan. Therefore, accurate knowledge of tryptophan requirement is important for dietary planning particularly for older adults. In 1998, our lab determined the tryptophan requirement in young women to be 4.01 mg/kg/day, with a safe intake at 5 mg/kg/day, using the Indicator Amino Acid Oxidation method. Since then, the investigators have determined the tryptophan requirement and safe level in healthy school-age children to be 4.7 and 6 mg/kg/day. The investigators have recently found the requirements of essential amino acids such as leucine and total sulfur amino acids in older adults and have found to be higher than young adults and a difference between the sexes. Thus, there is a need to determine the threonine requirement in older adults.

• Study Type: Interventional
• Enrollment (Estimated): 40
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Zhiyao Wang, MSc; Phone Number: 437 419 6224; Email: zhiyao.wang@sickkids.ca
• Study Contact Backup: Name: Mahroukh Rafii, BSc; Phone Number: 647 215 1201; Email: mahroukh.rafii@sickkids.ca

Study Locations

• Canada
  • Ontario
    • Toronto, Ontario, Canada, M5G 1X8
      • Recruiting
      • Hospital for Sick Children
      • Contact: Glenda Courtney-Martin, PhD; Phone Number: 416-814-5744; Email: glenda.courtney-martin@sickkids.ca

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Consent provided.
• Aged 60 to 90 years old.
• In good general health as evidenced by medical history, physical health and blood draw.
• Fasting blood glucose, hemoglobin A1c (HbA1c), urea, creatinine.
• Willingness to participate in the study.
• BMI <30 kg/m2.

Exclusion Criteria:

• Presence of chronic disease and/or acute illness known to affect protein/amino acid metabolism (e.g. HIV, diabetes, taking medications known to affect protein/AA metabolism (e.g. steroids).
• Inability to tolerate the diet (i.e. allergy).
• Significant weight loss during the past month or consumption of weight reducing diets.
• Significant caffeine consumption (>2 cups per day).
• Significant consumption of alcohol (>1 drink per day i.e. 1 beer or ½ glass of wine).
• Unwilling to have blood drawn from a venous access or using a ventilated hood indirect calorimeter for the purposes of the study.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Tryptophan in Adults >60y; Tryptophan levels, up to 7 levels, will be tested in a random order in all subjects	Other: Tryptophan; There are 7 different tryptophan test levels ranging from 0.5, 2, 4, 6, 8, 10, 12 mg.kg-1.day.1

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Determination of tryptophan requirement in adults >60 years of age.	To measure the tryptophan requirement investigators will collect breath samples from participants. From these samples, investigators will measure the amount of amino acids oxidized and how much is retained in the body when graded intakes of tryptophan are consumed by the participants consuming a controlled diet.	up to 24 months

Collaborators and Investigators

• Sponsor: The Hospital for Sick Children
• Collaborators: Canadian Institutes of Health Research (CIHR)
• Investigators: Principal Investigator: Glenda Courtney-Martin, PhD, RD, The Hospital for Sick Children

Study record dates

Study Major Dates

• Study Start (Actual): June 1, 2024
• Primary Completion (Estimated): July 1, 2025
• Study Completion (Estimated): December 1, 2025

Study Registration Dates

• First Submitted: February 21, 2024
• First Submitted That Met QC Criteria: February 21, 2024
• First Posted (Actual): February 28, 2024

Study Record Updates

• Last Update Posted (Actual): May 30, 2025
• Last Update Submitted That Met QC Criteria: May 23, 2025
• Last Verified: March 1, 2025

More Information

Terms related to this study

• Keywords: elderly; healthy; indicator amino acid oxidation; stable isotopes; tryptophan requirement
• Additional Relevant MeSH Terms: Psychotropic Drugs; Antidepressive Agents; Antidepressive Agents, Second-Generation; Tryptophan
• Other Study ID Numbers: 1000081113

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No