Which supplements should you take together?
Some supplements work better together. Some interfere with each other. This guide covers the key combinations — what to stack, what to separate, and when to take them.
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Ready-made stacks by goal
Foundation Daily Stack
The non-negotiables for UK adults
Sleep & Stress Stack
For those with high cortisol, anxiety, or poor sleep
Performance Stack
For regular gym-goers and athletes
Proven supplement combinations
Backed by clinical evidenceVitamin D3 increases calcium absorption, but K2 is required to direct that calcium to bones and away from soft tissues (arteries, kidneys). Taking D3 without K2 at high doses risks calcium depositing in the wrong places. Always pair them.
Magnesium is required to activate vitamin D. Without adequate magnesium, vitamin D supplementation is significantly less effective — the conversion enzyme from inactive to active D3 is magnesium-dependent.
Creatine replenishes ATP for high-intensity effort; protein provides amino acids for repair and growth. These complement each other perfectly — creatine doesn't provide amino acids, protein doesn't provide phosphocreatine. Together they cover both bases.
Caffeine alone causes jitteriness and anxiety that impairs performance. L-Theanine counteracts these effects via alpha brainwave induction, leaving clean focus without the crash. Multiple RCTs show this combination outperforms either alone on cognitive tasks.
Both are fat-soluble and taken with food. More importantly, they have complementary anti-inflammatory pathways — omega-3 via eicosanoid modulation, D3 via nuclear receptor activity. Together they support immune function, cardiovascular health, and cognitive performance synergistically.
Ashwagandha reduces cortisol via HPA axis modulation; magnesium activates GABA-A receptors to calm the nervous system. They work on different pathways but both reduce the physiological stress response, making them highly complementary for sleep and anxiety.
Vitamin C is a required cofactor for collagen synthesis — it hydroxylates proline and lysine, making them usable for collagen production. Taking collagen peptides without vitamin C wastes part of the benefit. Studies show the combination improves tendon repair and skin elasticity faster.
Zinc supports T-cell function and antiviral activity. Selenium supports glutathione production and natural killer cell activity. Both are required for optimal immune function and their effects are complementary rather than overlapping.
Combinations to avoid (or separate)
They compete for the same absorption transporter (DMT-1). Taking together reduces absorption of both significantly. Separate by at least 2 hours.
Calcium inhibits iron absorption. Do not take calcium supplements with iron supplements or iron-rich meals.
High-dose zinc supplementation (above 25mg) depletes copper over time by inhibiting absorption. If taking high-dose zinc, supplement with 1–2mg copper.
In very high doses, these can compete for absorption. In normal supplementation doses (under 500mg each), this is not a significant practical concern — just don't take both together in a single high-dose supplement.
The fat-soluble vitamins (A, D, E, K) compete for absorption and high-dose vitamin A can suppress vitamin D activity. Never exceed 1,500mcg RAE of vitamin A per day if supplementing D3.
Ashwagandha can increase thyroid hormone levels. If you take levothyroxine or other thyroid medication, consult your GP before supplementing ashwagandha.
When to take your supplements: a timing guide
- Vitamin D3 + K2 (fat-soluble — needs food)
- Omega-3 (fat-soluble, improves absorption with fat)
- B-vitamins (best tolerated with food)
- CoQ10 (fat-soluble, needs fatty meal)
- Creatine (any time — post-workout has slight edge)
- Collagen + vitamin C (30 mins pre-workout for joints)
- Protein (within 2 hours post-workout)
- L-Theanine (with or without caffeine, any time)
- Zinc (away from iron, calcium, and strong coffee)
- Iron (empty stomach for best absorption — take with vitamin C)
- Magnesium glycinate (1 hour before bed)
- Ashwagandha (with dinner or 1–2 hours before bed)
- Glycine (30 mins before bed in water)
- Casein protein (slow-release — maintains overnight MPS)
This guide is for educational purposes only. Always consult your GP or pharmacist before starting any new supplement, particularly if you take prescription medication. Some supplements interact with medications — always disclose what you're taking to your healthcare provider.
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