NZ GLP-1 hub · Supplements · 5 November 2026 · Peer-reviewed
Multivitamins: what they can and can't do when you're eating less
General information, not advice. Supplements can interact with medicines. Talk to your doctor or pharmacist before starting one, especially if you take other medicines, are pregnant, or have a kidney or liver condition.
Why people take them
A multivitamin combines several vitamins and minerals in one tablet. People take them for various reasons, including when they think their diet falls short.
Why it comes up with GLP-1 medicines
Eating far less food usually means eating fewer vitamins and minerals too. Studies of people on GLP-1 medicines have found shortfalls in iron, calcium, vitamin D and vitamin B12. A 2025 joint advisory from US obesity and nutrition societies on supporting GLP-1 therapy flagged micronutrient intake as a priority and said supplementation may be needed for some people.
What the evidence shows
Multivitamins might benefit certain groups of people, and a blood test can show whether you're one of them. For preventing heart disease or cancer, the US Preventive Services Task Force found the evidence insufficient.
What it doesn't do
It doesn't replace food: it supplies vitamins and minerals, not protein or fibre. Multivitamins also have no standard definition, so the nutrients and amounts vary widely. One may not cover a nutrient you're short of, so check with your pharmacist.
Who should be careful
- →Some multivitamin users get too much vitamin A, iron or zinc. People with hemochromatosis, an inherited condition, can build up toxic levels of iron.
- →Pregnancy: too much vitamin A can increase the risk of birth defects. Talk to your midwife or doctor.
- →Blood thinners such as warfarin: talk to your doctor or pharmacist before taking any supplement containing vitamin K.
Food first, then a test
A blood test through your GP shows actual shortfalls. Our guide to eating well when your appetite is smaller covers food quality on a small intake.
Sources
- NIH Office of Dietary Supplements — Multivitamin/mineral supplements, health professional fact sheet
- Mozaffarian D et al. — Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from four US societies (Obesity) · 2025-05-30
- Urbina J et al. — Micronutrient and nutritional deficiencies associated with GLP-1 receptor agonist therapy: a narrative review (Clinical Obesity) · 2026
- NIH Office of Dietary Supplements — Iron, consumer fact sheet
Review: Founder review via PR merge. General information only; no recommendations, brands, prices or product links; sources verified 5 Nov 2026.
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