Supplements for women: what the evidence supports

Iron, vitamin D, omega-3, calcium, folate and creatine, sorted by what the trials in women actually found, plus why creatine was understudied in women for so long.

Key takeaways

  • Most supplement trials were run in men, and creatine is the clearest example of a well evidenced supplement that women were told to skip.
  • Iron is the most common genuine deficiency in menstruating women and the one worth measuring rather than guessing, because too much iron is also a problem.
  • Vitamin D dosed to a measured level, adequate protein, calcium mainly from food, and omega-3 cover most of the useful ground.
  • Calcium and vitamin D reduce fracture risk modestly at best in generally healthy women, which is why they are a floor rather than a bone strategy.
  • Folate matters before conception, not after a positive test, because neural tube closure happens in the first weeks.

Most supplement research was done in men, and the gaps show up in the recommendations women get.

Where trials in women exist, they point at a shorter and more specific list than the aisle suggests.

The research gap, stated plainly

For decades most exercise and supplement research recruited men, partly to avoid accounting for the menstrual cycle. The result is that advice given to women is often extrapolated rather than tested. Where trials in women do exist, they sometimes overturn the assumption.

Creatine is the clearest case. Women were widely told it would cause bloating and was for male athletes. The reviews in women report improvements in strength and exercise performance, no meaningful fat gain, and interest in effects on mood and bone that is still being studied.

What has evidence in women

  • Creatine monohydrate, 3 to 5 g daily. Studied in women across the lifespan, with the strongest effects alongside resistance training.
  • Iron, if ferritin is low. Heavy periods, pregnancy and endurance training are the common causes, and fatigue with low ferritin responds to correction in a way it does not otherwise.
  • Vitamin D, dosed to a measured 25-hydroxyvitamin D level.
  • Protein, roughly 1.2 to 1.6 g per kg per day if you train, and per meal amounts matter as much as the daily total.
  • Omega-3, by intake or an omega-3 index.
  • Folate, at least 400 micrograms daily for anyone who could become pregnant, started before conception.
  • Iodine, which is easy to fall short on if you use non-iodized salt and eat little dairy or seafood.

Iron, and why guessing is the wrong approach

Iron deficiency is common in menstruating women and is a real cause of fatigue, poor exercise tolerance and hair shedding. It is also the deficiency most often self-treated blind, and iron overload causes its own harm, so this is a measure first situation.

Ferritin is the practical marker, read alongside hemoglobin and, when inflammation is present, with the understanding that ferritin rises with inflammation and can look falsely reassuring. That nuance is exactly why a panel beats a single number.

Calcium, vitamin D and bone

The Women's Health Initiative randomized more than 36,000 postmenopausal women to calcium plus vitamin D and found no significant reduction in hip fracture in the primary analysis, with a small increase in kidney stones. DO-HEALTH, in 2,157 older adults, found no benefit of vitamin D or omega-3 on a set of outcomes including fracture.

The reasonable reading is that calcium and vitamin D are a floor, best met mainly through food and a measured vitamin D level, and that the things that actually build and hold bone are loading it and having enough protein and muscle around it.

What to measure

  • Ferritin, hemoglobin and a full blood count.
  • 25-hydroxyvitamin D.
  • TSH with free T4, because thyroid disease is meaningfully more common in women.
  • Fasting insulin and glucose for HOMA-IR, plus HbA1c.
  • A lipid panel with ApoB where available.
  • Body composition, because weight alone hides the muscle to fat shift that matters.

What this means for you

Measure iron and vitamin D rather than guessing, get enough protein, and take creatine if you train. Most of what is marketed specifically to women is a more expensive version of a general recommendation.

References

  1. Smith-Ryan AE, et al., creatine supplementation in women's health, a lifespan perspective, Nutrients, 2021
  2. de Guingand DL, et al., risk of adverse outcomes in females taking oral creatine monohydrate, a systematic review, Nutrients, 2020
  3. Jackson RD, et al., calcium plus vitamin D supplementation and the risk of fractures (Women's Health Initiative), New England Journal of Medicine, 2006
  4. Bischoff-Ferrari HA, et al., effect of vitamin D, omega-3 and exercise on functional decline and outcomes in older adults (DO-HEALTH), JAMA, 2020
  5. Manson JE, et al., vitamin D supplements and prevention of cancer and cardiovascular disease (VITAL), New England Journal of Medicine, 2019
  6. Camaschella C, iron deficiency, Blood, 2019
  7. US Preventive Services Task Force, folic acid supplementation for the prevention of neural tube defects, JAMA, 2017

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