Men over 40 taking GLP-1 medications face unique nutritional challenges that may necessitate careful consideration of multivitamin supplementation. GLP-1 receptor agonists such as semaglutide and liraglutide, licensed in the UK for type 2 diabetes and weight management, work by reducing appetite and slowing gastric emptying. Whilst therapeutically beneficial, these effects often lead to significantly reduced food intake, potentially compromising micronutrient status. Age-related physiological changes—including declining muscle mass, reduced bone density, and altered metabolic function—further compound nutritional requirements. This article examines the specific vitamin and mineral needs for men in this demographic, explores how GLP-1 therapy affects nutrient intake and absorption, and provides evidence-based guidance on selecting appropriate supplementation whilst prioritising food-first approaches and medical oversight.

Nutritional Needs for Men Over 40 on GLP-1 Medications

Men over 40 experience gradual physiological changes that alter their nutritional requirements, including decreased muscle mass, reduced bone density, and changes in metabolic function. When combined with GLP-1 receptor agonist therapy, these nutritional considerations become particularly important.

GLP-1 medications work by mimicking the incretin hormone glucagon-like peptide-1, which regulates appetite, slows gastric emptying, and improves glycaemic control. In the UK, semaglutide (Wegovy) and liraglutide (Saxenda) are licensed for weight management, while semaglutide (Ozempic) and liraglutide (Victoza) are approved for type 2 diabetes. Whilst therapeutically beneficial, these medications often result in significantly reduced food intake, which can inadvertently lead to inadequate intake of essential micronutrients.

Key nutritional priorities for this demographic include:

• Protein intake – Important for preserving lean muscle mass during weight loss, with clinical recommendations often suggesting 1.2–1.5g per kilogram of body weight daily during weight loss (compared to the UK Reference Nutrient Intake of 0.75g/kg/day), provided kidney function is normal

• Calcium and vitamin D – Critical for bone health as bone density naturally declines with age

• B vitamins – Particularly B12, which supports neurological function and energy metabolism

• Magnesium and potassium – Important for cardiovascular health and muscle function

The combination of age-related changes and medication-induced appetite suppression creates a scenario where micronutrient deficiencies may develop more readily. This makes strategic nutritional planning, including potential supplementation, an important consideration for men in this category. However, food-first approaches should always be prioritised where possible, with supplements serving as an adjunct rather than replacement for a balanced diet.

How GLP-1 Treatments Affect Vitamin and Mineral Absorption

GLP-1 receptor agonists exert their primary effect by slowing gastric emptying—the rate at which food moves from the stomach into the small intestine. This delayed transit time is central to the medications' ability to promote satiety and improve post-prandial glucose control. However, there is limited evidence that this mechanism significantly affects nutrient absorption in most patients.

The small intestine is the primary site for nutrient absorption, and the rate of gastric emptying can affect how efficiently certain vitamins and minerals are taken up. Fat-soluble vitamins (A, D, E, and K) require adequate bile acid secretion for optimal absorption. While the altered gastrointestinal transit may theoretically affect their bioavailability in some individuals, clinically significant malabsorption has not been established as a common concern with GLP-1 medications.

Water-soluble vitamins, including the B-complex vitamins and vitamin C, are generally absorbed throughout the small intestine. The delayed gastric emptying associated with GLP-1 therapy does not appear to substantially impair their absorption, though reduced overall food intake naturally decreases dietary vitamin intake.

Mineral absorption presents a more complex picture. Iron absorption occurs primarily in the duodenum and is influenced by gastric acid secretion and transit time. Calcium absorption is similarly pH-dependent and occurs throughout the small intestine. Whilst GLP-1 medications do not directly alter gastric acid production, the reduced food volume and altered eating patterns may indirectly affect mineral bioavailability.

It is important to note that most concerns about nutrient status with GLP-1 therapy relate to reduced dietary intake rather than direct malabsorption. The medications' appetite-suppressing effects mean patients simply consume less food, thereby obtaining fewer micronutrients from their diet. Additionally, the effect on gastric emptying may attenuate over time with continued treatment. This distinction is clinically relevant when considering supplementation strategies.

Key Vitamins and Minerals to Consider While Taking GLP-1

Men over 40 taking GLP-1 medications should pay particular attention to several micronutrients that may become deficient due to reduced caloric intake and specific age-related requirements.

Vitamin B12 (cobalamin) is essential for neurological function, red blood cell formation, and DNA synthesis. Men over 40 already face increased risk of B12 deficiency due to reduced gastric acid production with age. When combined with the reduced meat and dairy intake often seen with GLP-1 therapy, deficiency risk increases further. The UK Reference Nutrient Intake is 1.5 micrograms, though higher doses (25–100 micrograms) are often included in multivitamin formulations to ensure adequate absorption. Men with type 2 diabetes taking metformin may have additional risk of B12 deficiency, as this medication can reduce absorption over time.

Vitamin D and calcium work synergistically to maintain bone health. Men over 40 experience gradual bone density loss, and weight loss may affect bone health in some individuals. UK health authorities recommend 10 micrograms (400 IU) of vitamin D daily, particularly during autumn and winter months. Calcium requirements remain at 700mg daily, though men on GLP-1 therapy may struggle to meet this through diet alone if dairy intake is reduced.

Magnesium supports over 300 enzymatic reactions, including muscle function, nerve transmission, and glucose metabolism. The recommended intake is 300mg daily for men. Magnesium deficiency can manifest as muscle cramps, fatigue, and mood changes—symptoms that may be mistakenly attributed to the GLP-1 medication itself.

Iron requirements for men are generally lower than for premenopausal women (8.7mg daily), but reduced red meat consumption on GLP-1 therapy may necessitate attention to iron status, particularly in men with existing anaemia or those following plant-based diets.

Zinc is crucial for immune function, wound healing, and normal hormonal function. The recommended intake is 9.5mg daily, and deficiency may occur with reduced meat and shellfish consumption. Other important micronutrients include vitamin C (40mg daily), vitamin E (4mg daily), and selenium (75 micrograms daily), all of which support immune function and cellular health.

Vitamin A intake should be monitored carefully, as high retinol intake (>1.5mg daily from supplements and food combined) may increase fracture risk in older adults. Men taking supplements should be cautious about consuming liver products, which are very high in retinol.

Choosing a Multivitamin: What to Look for on GLP-1 Therapy

Selecting an appropriate multivitamin whilst taking GLP-1 medications requires consideration of several factors beyond standard formulations marketed to men over 40.

Dosage and bioavailability are paramount. Look for formulations that provide approximately 100% of the Nutrient Reference Value (NRV) for most vitamins and minerals, rather than mega-doses that offer no additional benefit and may cause adverse effects. Pay particular attention to the forms of nutrients included: methylcobalamin or cyanocobalamin for B12, cholecalciferol (vitamin D3) rather than ergocalciferol (D2), and minerals in forms that support good absorption. Different mineral forms may have varying absorption rates, though this varies by individual mineral and dosage.

Tablet size and formulation become especially relevant for patients experiencing GLP-1-related gastrointestinal effects. Large tablets may be difficult to swallow or may exacerbate nausea. Consider:

• Smaller tablets or capsules that are easier to swallow

• Liquid or chewable formulations if tablets cause discomfort

• Divided doses (twice daily rather than once daily) to reduce gastrointestinal burden

Quality assurance is essential. In the UK, food supplements are regulated by the Food Standards Agency (FSA). Look for products from reputable manufacturers that comply with food safety standards. While supplements are not pre-approved by regulatory authorities, responsible manufacturers will have quality control measures in place.

Avoid excessive iron unless specifically advised by your GP, as men over 40 rarely require iron supplementation and excessive intake may increase oxidative stress. Similarly, be cautious of formulations with high doses of vitamin A (as retinol), as this can accumulate in the body and potentially increase fracture risk in older adults.

Important safety considerations include vitamin K content if you take warfarin (consistent intake is important for stable anticoagulation), and timing of mineral-containing supplements if you take levothyroxine, tetracyclines, or quinolone antibiotics (separate by at least 4 hours for levothyroxine and 2 hours for antibiotics). High-dose biotin supplements may interfere with certain laboratory tests, so always inform healthcare providers about supplements you take before blood tests.

Potential Interactions Between Multivitamins and GLP-1 Medications

Direct pharmacological interactions between standard multivitamin supplements and GLP-1 receptor agonists are uncommon, but several considerations warrant attention to ensure optimal therapeutic outcomes and patient safety.

Timing of administration may influence both medication efficacy and supplement absorption. GLP-1 medications are typically administered subcutaneously at specific times (often morning or evening, depending on the formulation), whilst multivitamins are usually taken orally with food. There is no official guidance suggesting that multivitamins interfere with GLP-1 absorption or action, as these medications are injected rather than taken orally. However, taking multivitamins with a small meal may improve tolerability and absorption of fat-soluble vitamins.

Gastrointestinal side effects represent the most common area of concern. Both GLP-1 medications and certain vitamins/minerals can cause nausea, with iron and magnesium being particular culprits. Taking a multivitamin during the initial titration phase of GLP-1 therapy may compound nausea. Some patients find that introducing supplementation gradually once gastrointestinal symptoms have stabilised improves tolerance, though this should be individualised based on symptoms rather than following a fixed timeline.

Mineral interactions within the multivitamin itself deserve consideration. Calcium can interfere with iron absorption when taken simultaneously, though the clinical significance in the context of a daily multivitamin is generally minimal. Zinc and copper compete for absorption, so formulations should contain both in appropriate ratios (typically 15:1 zinc to copper).

Blood glucose monitoring remains important for patients with diabetes taking GLP-1 medications. Whilst multivitamins do not directly affect blood glucose, some formulations contain small amounts of sugar or carbohydrate in coatings or fillers. This is rarely clinically significant but may be relevant for patients with very tight glycaemic control requirements.

Warfarin users should note that vitamin K in multivitamins may affect INR (International Normalised Ratio). Consistent daily intake is preferable to erratic use. Your healthcare provider may need to monitor your INR more closely when starting or stopping supplements containing vitamin K.

There is no evidence that standard multivitamin supplementation reduces the efficacy of GLP-1 medications or increases the risk of adverse effects when used appropriately. However, individual responses vary, and any new symptoms following supplementation initiation should be reported to your healthcare provider or through the MHRA Yellow Card scheme.

When to Speak with Your GP About Supplementation

Whilst over-the-counter multivitamins are widely available and generally considered safe, men over 40 taking GLP-1 medications should consult their GP or prescribing clinician before starting supplementation in several specific circumstances.

Before initiating any supplementation, discuss your plans with your healthcare provider, particularly if you have:

• Pre-existing medical conditions such as kidney disease, liver disease, or haemochromatosis (iron overload disorder)

• Multiple medications that may interact with high-dose vitamins or minerals

• A history of kidney stones, as calcium and vitamin D supplementation may increase recurrence risk

• Planned surgical procedures, as some supplements may need to be discontinued perioperatively

Symptoms suggesting possible deficiency warrant medical evaluation rather than self-treatment. Contact your GP if you experience:

• Persistent fatigue, weakness, or shortness of breath (possible anaemia)

• Numbness, tingling, or balance problems (possible B12 deficiency)

• Muscle cramps, spasms, or irregular heartbeat (possible magnesium or potassium deficiency)

• Bone pain or frequent fractures (possible vitamin D or calcium deficiency)

• Poor wound healing or frequent infections (possible zinc or vitamin C deficiency)

Seek urgent medical attention (call 111 or 999 as appropriate) for severe palpitations, chest pain, fainting, or signs of severe allergic reaction. Never self-supplement with potassium without medical supervision.

Your GP may arrange blood tests to assess nutritional status before recommending supplementation. Common investigations include full blood count, vitamin B12, folate, vitamin D (25-hydroxyvitamin D), and ferritin. These tests provide objective evidence of deficiency and allow for targeted, therapeutic-dose supplementation rather than empirical multivitamin use.

Targeted monitoring is advisable for men on long-term GLP-1 therapy, particularly those who have lost significant weight or have specific risk factors. For those with type 2 diabetes, nutritional assessment may be incorporated into routine diabetes reviews. Those taking metformin long-term should be particularly vigilant about B12 status, as this medication can reduce absorption.

Finally, if you experience new or worsening symptoms after starting a multivitamin—including nausea, abdominal pain, constipation, or allergic reactions—discontinue the supplement and consult your GP promptly. Suspected adverse reactions to supplements or medications can be reported through the MHRA Yellow Card scheme.

Frequently Asked Questions