What actually improves egg and sperm quality?

"Egg quality" is the phrase that sells more supplements than any other in fertility. Here's what's behind each of the usual recommendations, rated honestly. The short version: a few are worth considering, none is transformative, and the three months people spend waiting for a supplement to work are sometimes three months that mattered.

For eggs

• Emerging evidence CoQ10. The most studied of them. What the trials found →
• Limited or mixed DHEA. Possibly helpful for poor responders in small trials; it is a hormone with hormone side effects, and no professional body recommends it routinely. A clinic recommending it for low reserve is making a defensible call; buying it yourself is not the same thing.
• Emerging evidence Melatonin. Studied mostly as an IVF add-on, in small trials with mixed results. Cochrane's review of antioxidants in women rates this whole area low to very low certainty. Melatonin also affects sleep timing, so it isn't neutral.
• Emerging evidence NAC and other antioxidants. Same picture: small studies, inconsistent results, no guideline endorsement.
• Limited or mixed Vitamin D, if you're deficient. The evidence →
• Emerging evidence Diet pattern does about as much as any supplement, with better evidence behind it. What was actually studied →

What no supplement does: change the age of your eggs. Age remains the strongest predictor of egg quality, which is why a timeline conversation is worth more than a shelf of bottles.

Limited or mixed For sperm

This is the clearest example on the site of two good sources disagreeing.

The MOXI trial gave men with abnormal semen results a combined antioxidant — vitamins C, E and D, selenium, L-carnitine, zinc, folic acid and lycopene — for three to six months. Semen measures did not improve. Live births were 15% in the supplement group and 24% on placebo, though the trial stopped early and was too small to settle the birth question by itself.

Cochrane's 2022 review pooled 90 trials in over 10,000 men and found antioxidants may increase live births — while rating that conclusion very low certainty, which in plain terms means the answer could easily reverse with better trials.

So: not nothing, not proven, and not a substitute for finding out whether there's something specific to treat.

What has better evidence than any of these

• Strong evidence A proper semen analysis, and a urologist if it's abnormal. A varicocele, an infection, a hormone problem or a medication can be treated. A supplement can't fix any of them. Testing both partners →
• Moderate evidence Heat. Sperm production is temperature-sensitive: hot tubs, saunas and a laptop on the lap for hours are worth cutting during the two to three months before trying, since that's how long a cycle of sperm production takes.
• Strong evidence Not smoking, and not vaping. Both partners.
• Insufficient evidence Sleep. What's been shown →

Questions to ask

"Is there anything specific in my results to treat, rather than supplement?" "If I take this for three months, what would we expect to change, and how would we measure it?" "Does waiting three months cost me anything, given my age and history?"