The Most Common Nutrient Deficiencies in Active People

Three things separate an active body from a sedentary one when it comes to nutrients. You lose minerals such as iron, magnesium and calcium in sweat. Hard training raises the turnover of red blood cells and muscle tissue, so you use more of the raw materials that build them. And many active people eat in a way that fights their intake, whether that is cutting calories to lean out, skipping meals around a busy training schedule, or dropping whole food groups.

The reason these gaps stay hidden is that the symptoms are boring and familiar. Low iron feels like being tired and having no snap in your legs. Low vitamin D shows up as more colds and achier recovery. Low magnesium can mean cramps and poor sleep. Every one of those could just as easily be a hard training week, which is exactly why people push on for months before they think to look.

Iron carries oxygen in your blood, so when it drops, your engine loses power. Active people lose more of it than most: through menstruation, through tiny amounts of gut bleeding in endurance sport, through sweat, and through a training-driven rise in a hormone called hepcidin that temporarily blocks iron absorption after hard sessions. Menstruating women and endurance runners sit at the top of the risk list, with review data putting iron deficiency at 15 to 35 percent of female athletes and 5 to 11 percent of male athletes.

The number that matters is not just haemoglobin, which flags full-blown anaemia, but ferritin, which reflects your iron stores. You can feel flat and recover poorly with low ferritin long before anaemia shows up. That is why a plain tired legs complaint that will not lift with rest is worth a blood test rather than another deload.

Your skin makes vitamin D from sunlight, so the people who fall short are predictable: anyone who trains indoors, lives far from the equator, has darker skin, or covers up outdoors. Through winter, most of the population in northern countries cannot make enough from sun alone. Vitamin D matters for active people because it supports muscle function, bone health and the immune system, and low levels track with more stress fractures and more time lost to minor illness.

Food only contributes a little, since few foods carry much vitamin D, mainly oily fish, egg yolks, and fortified products such as some plant milks, dairy and cereals. That is why sunlight and, when it is scarce, a supplement do most of the work. It is one of the few nutrients where relying on diet alone genuinely struggles to cover the gap for a lot of people, which is exactly why testing is so useful here.

Magnesium sits inside hundreds of reactions that make energy and let muscles contract and relax. You lose some in sweat, and intakes are commonly below target in people eating a lot of refined food. The classic signs of running low, cramps, twitchy muscles, poor sleep and irritability, are vague enough to blame on training, which is the recurring theme of this whole list.

The good news is that magnesium is easy to top up from food, and the best sources are ordinary staples. You rarely need a pill if a few of these are regulars on your plate.

• Pumpkin seeds, almonds and cashews, a handful is a serious dose
• Black beans, edamame and other legumes, which double as protein
• Wholegrains such as oats, brown rice and wholemeal bread
• Dark leafy greens like spinach and Swiss chard
• Dark chocolate, genuinely a decent source at 70 percent and above

Vitamin B12 keeps your nerves and red blood cells working, and it is the one nutrient that plant foods do not reliably provide. If you eat a vegan or mostly plant-based diet, this is not a flaw in the diet, it is simply a nutrient you cover a different way: through fortified foods such as some plant milks, nutritional yeast and cereals, or a cheap, effective supplement. Plenty of thriving athletes eat entirely plant-based and never run short, precisely because they plan this one deliberately rather than leaving it to chance.

Calcium protects the bones that your training loads every day, and it is another nutrient worth checking if you avoid dairy. It is entirely coverable from plants: fortified plant milks and yoghurts, tofu set with calcium, and greens such as kale and bok choy all count, alongside dairy and canned fish with soft bones if you eat them. The aim is a couple of solid calcium sources most days, from whichever foods suit you.

Because every deficiency on this list feels like tiredness, you cannot diagnose it by how you feel. The honest move is to test the specific markers rather than throwing a stack of supplements at the problem and hoping.

1. Start with a basic panel. Ask your doctor for a full blood count plus ferritin, vitamin D, and B12 if you eat few animal foods. This covers the common culprits in one draw.
2. Read ferritin, not just haemoglobin. You can feel flat with low iron stores well before anaemia appears, so the ferritin number is the early warning you want.
3. Fix food first. For most gaps, adjusting what is on your plate closes the shortfall. Supplements are for confirmed deficiencies or genuinely hard-to-reach nutrients like B12 on a vegan diet.
4. Retest before you assume it worked. Give a change a few months, then recheck the same marker. Guessing whether it helped is how people end up over-supplementing something they never lacked.