Supplements, what the evidence actually supports

Supplements are adjuncts to, not replacements for, a nutrient-rich diet, adequate sleep, appropriate movement, and emotional wellbeing. Starting any relevant supplement at least 3 months before trying to conceive aligns with the 75–85 day egg and sperm development timeline.

The fertility supplement market is enormous and lightly regulated. Social media is full of confident claims. The actual evidence, unglamorously, is smaller, and mostly supports a short list.

Methylfolate (5-MTHF) is the biologically active form. Approximately 10–14% of the UK population carry an MTHFR gene variant that reduces the enzyme converting folic acid into its active form. For most women without known MTHFR variants or recurrent pregnancy loss, either form of folate at 400–800 micrograms is appropriate.

The best available trial found no significant difference in pregnancy outcomes between methylfolate and folic acid, even in MTHFR carriers. Discuss with a GP if there is a history of recurrent pregnancy loss.

Vitamin D acts more like a hormone than a typical vitamin, influencing over 2,000 genes. In the UK, northern latitude means sun exposure is insufficient for natural synthesis October to March. For people with darker skin tones, who cover skin for religious or cultural reasons, or who are overweight, deficiency is significantly more common, 55–60% of UK South Asians have severe deficiency.

Roles in fertility: supports menstrual cycle regulation, healthy development of the uterine lining, egg maturation and quality, and in men, testosterone production and sperm motility.

Myo-inositol has Cochrane-reviewed, Level 1 evidence for ovulation induction in PMOS. Typical dose: 2–4 g daily, often in combination with folic acid and sometimes d-chiro-inositol (40:1 myo:DCI ratio reflects the natural ovarian balance).

Particularly relevant for the insulin-resistant PMOS subtype. Unfer V et al (2017) and Zeng L, Yang K (2018) show modest but consistent improvements in cycle regularity, ovulation rate, and insulin markers over 3–6 months.

• Iron and ferritin correction where deficient (blood test first, heavy periods and vegetarian diets create silent gaps; treat ferritin below 30 µg/L) • B12 for vegetarians and vegans, common deficiency, cheap to correct • Omega-3 (EPA/DHA) 1–2 g daily, modest fertility evidence, good general-health evidence • CoQ10 for women over 35 or poor-responder IVF, some supportive evidence, discuss with clinic

Rule of thumb: if a product promises to 'reverse PMOS', 'cure endometriosis', or 'guarantee pregnancy', walk away.