This is a randomized, double-blind, placebo-controlled, parallel-group, study evaluating the effect of a Qualia Vitamin C+ formulation on Whole Blood Vitamin C levels in the blood of healthy adults aged 25 years or older that have suboptimal vitamin C blood levels (i.e., 0.4 - 0.9 mg/dL) and those with adequate vitamin C blood levels (≥0.9 mg/dL). Approximately 152 (76 in the suboptimal stratum and 76 in the adequate stratum) participants will be randomized to one of two study arms: Qualia Vitamin C+ or placebo. Each participant will take two capsules of their assigned product once daily in the morning, with or without food, over a 28-day period. The primary outcome is the change in blood vitamin C levels in the suboptimal stratum, assessed via lab blood collection at baseline and study completion. Secondary endpoints include the change in blood vitamin C levels, assessed via lab blood collection at baseline and study completion in the entire group, questionnaires measuring health-related Quality of Life and fatigue (RAND-36 and the FACIT-Fatigue Scale), the Single-item Assessment of Immune Fitness, evaluation of safety and tolerability, and an Overall Experience Questionnaire. Further, a sub-group analysis of fatigued participants meeting at least mild to moderate fatigue as measured by the FACIT-Fatigue will be a secondary objective. The NCI Fruits and Vegetable Screener - All-Day Screener will also be used to assess intake at baseline and study completion. All assessments, including electronic questionnaires, are completed remotely without in-person visits.

Design: Randomized Double-Blind Placebo-Controlled Parallel 4-Armed Trial (4 arms) with 1:1:1:1 allocation, stratified by gender, age, and baseline vitamin C levels. Arms: (1) Suboptimal Qualia Vitamin C+, (2) Suboptimal Placebo, (3) Adequate Qualia Vitamin C+, and (4) Adequate Placebo. Participants will be stratified by gender and age at screening before being randomly assigned in a 1:1:1:1 ratio to one of the two study arms per stratum. Each participant will take two capsules of their assigned product daily in the morning, with or without food, for 28 consecutive days. Participants will receive a 28-day supply (56 capsules) of their assigned intervention. The active product Qualia Vitamin C+ delivers 500 mg total vitamin C per daily serving (2 capsules) and contains a blend of Vitamin C (from liposomal vitamin C, mineral ascorbates, and fruit extracts), bioflavonoids, and ferulic acid. The placebo contains inert rice powder in a vegetable/cellulose capsule. Blood vitamin C levels will be measured via blood draws through Ulta Labs, which uses licensed blood draw centers operated by Quest Diagnostics. To maintain double-blinding, a designated Qualia Life Sciences staff member independent of the research team will assign and label all study products as A or B. Both participants and study personnel will remain blinded to group assignments until study completion. The primary analysis will be ANCOVA on Day 28 serum vitamin C in the suboptimal stratum, with baseline serum vitamin C, age, and sex as covariates and treatment arm as the factor of interest. Total enrollment: 152.

Inclusion Criteria:

• Provide voluntary, written, informed consent to participate in the study.
• Agree to provide a valid cell phone number and are willing to receive communications through text.
• Can read and write English.
• Willing to complete questionnaires, records, and diaries associated with the study.
• Healthy male and female participants aged 25 to 75 years old.
• Willing to go to an Ulta Labs Patient Service Center location for a Blood Vitamin C Test (baseline and Day 29) and located within a convenient distance of participating locations. The services offered by Ulta Lab Tests are available only in the United States and not to residents of the states of New Jersey, New York, and Rhode Island.
• Willing to avoid starting new or stopping any existing dietary supplements throughout the study.
• Willing to maintain a consistent diet throughout the study.

Exclusion Criteria:

• Women who are pregnant, breastfeeding, or planning to become pregnant or start breastfeeding during the trial.
• Known food intolerances/allergy to any ingredients in the product.
• Having any of the following conditions: Psychiatric conditions, neurologic disorders, endocrine disorders, cancer.
• Having had a significant cardiovascular event in the past 6 months.
• Taking MAO inhibitors, SSRIs, or any other psychiatric or neurological medicines.
• On immunosuppressive therapy.
• Adults lacking capacity to consent.

To maintain double-blinding, a designated Qualia Life Sciences staff member independent of the research team will assign and label all study products as A or B. Both participants and study personnel will remain blinded to group assignments until study completion. Unblinding will occur only after all study data have been collected and finalized.