The supplement market for fertility is large, and the evidence base behind most of it is thin.
That is not a reason to take nothing. It is a reason to know which small number of things have real data behind them, take those, and ignore the rest, which is a harder instruction to follow than it sounds when the products are everywhere.
Folate is the one supplement where the evidence is strongest and the recommendation is universal. The standard UK guidance is 400 micrograms daily from at least three months before conception and through the first trimester; 5mg is recommended for higher-risk groups (previous neural tube defect, BMI over 30, diabetes, certain medications).
This is about neural tube development, not fertility per se, but it's the intervention with the clearest evidence and lowest risk. If you have variants in the MTHFR gene affecting folate metabolism, methylfolate is a better-absorbed form and readily available.
Vitamin D deficiency is extremely common in the UK and is associated with worse IVF outcomes in several cohort studies. Vitamin D receptors are found in endometrial and ovarian tissue, and the mechanistic plausibility is real even if the evidence from trials is still building.
1,000 to 2,000 IU daily is a reasonable maintenance dose through autumn and winter; if you've never checked your level, that's worth doing once. Most people in northern latitudes are deficient at some point each year regardless of diet.
CoQ10 is involved in mitochondrial energy production, and eggs are among the most mitochondria-dependent cells in the body. Mitochondrial function in eggs does decline with age, and the evidence across multiple small trials is consistent in showing that supplementation is associated with improved markers of egg quality and modest improvements in embryo development, particularly in women over 35 or with diminished ovarian reserve.
The evidence is not definitive, there is no large RCT, but the direction is consistent and the risk is very low. 200 to 400mg of ubiquinol (the active, reduced form) daily is the form most consistently used in the supporting studies. The same mechanistic logic applies to sperm quality, and several meta-analyses show modest improvements in motility and morphology.
Omega-3 fatty acids affect membrane composition in eggs and sperm, and the UK diet is generally deficient in EPA and DHA.
The fertility-specific evidence is reasonable but not strong. The case for supplementation is better in pregnancy, preterm birth risk, fetal neurodevelopment, and that alone makes 1 to 2g daily of EPA and DHA from a quality fish oil or algae-based equivalent reasonable for anyone in the trying-to-conceive window.
The short list, and where to stop
Build the four-item stack and stop there: folate or methylfolate from at least three months before you want to conceive; vitamin D 1,000 to 2,000 IU daily through autumn and winter; CoQ10 200 to 400mg ubiquinol if you're over 35, have low AMH, or your male partner has any semen analysis flag; a quality omega-3 at 1g EPA+DHA. Everything else requires a specific reason, a deficiency, a diagnosis, a clinical recommendation. Whether a prenatal multi-vitamin is useful depends on your starting point. If you are vegan or vegetarian, a multi that includes B12 and iodine closes a gap that diet alone often doesn't – both matter in early pregnancy and neither is reliably covered by plant-based eating.
If you have a history of heavy periods or have never had your ferritin checked, iron is worth testing before supplementing rather than assuming; high-dose iron without a confirmed deficiency adds no benefit and can cause symptoms. If you carry variants in the MTHFR gene, a multi formulated with methylfolate rather than folic acid is a reasonable choice.
Outside these groups, the four-item stack generally covers the bases – but if you're unsure where you land, that's exactly the question to take to your GP. When a product makes a claim, the question to ask is 'what is the trial that shows this' rather than 'does this sound plausible'.