When you're taking your daily vitamin, you may have the handiwork of a female scientist in your hands. Marguerite Davis co-discovered the existence of vitamin A in 1913, Katherine Bishop was part of the team that discovered vitamin E in 1922, and Lucy Wills was the sole discoverer of folic acid.

It's important to remember that vitamins are meant to be ingested through food — or, in the case of vitamin D, absorbed through sunlight on the skin — rather than given through pills in healthy people. That's how our bodies are meant to work: with pills as a stopgap, not as a necessity. A study in 2019 found that multivitamins weren't as effective as plain old good diet at achieving longevity. "There are beneficial associations with nutrients from foods that aren't seen with supplements," the lead study author Dr. Fang Fang Zhang said in a press release.

If you're experiencing a deficiency in a vitamin, you may be tempted to run for the supplement aisle — but fixing your diet first is actually the proper step, say experts. Dr. Penny Kris-Etherton, Distinguished Professor of Nutrition at Pennsylvania State University’s College of Health and Human Development, told the American Heart Association that, “Nutritionists recommend food first because foods provide a variety of vitamins and minerals and also dietary factors that are not found in a vitamin or mineral supplement." Supplements might seem like a quick fix, but they could actually be a less efficient way of upping your vitamin levels.

Post-menopausal women should take vitamin K2 to help with their bone mineral density, as they might help with reducing bone injuries and fractures, according to studies collected by Healthline. They point out, however, that some studies have shown this effect is a bit inconsistent — which could be to do with other health factors, genetics, or other elements we don't yet understand.

Multivitamins aren't going to help your heart out. That's the latest news from a series of studies in 2018, which concluded that daily multivitamins didn't reduce risk of heart disease, stroke or heart attacks, and didn't seem to affect heart health in general at all. If you need to improve your heart health, other options are going to be more effective.

We all know that we get vitamin D through absorbing it through our skin — but a study in 2017 found that it might also be helpful when taken in supplement form shortly after experiencing a sunburn. It created some anti-inflammatory action and helped reduce swelling and pain, so if you've been burned, reach for both the aloe vera and the vitamin D.

Women are far more likely than men to have a fibromyalgia diagnosis, and vitamin D may prove to be helpful for managing symptoms, according to a 2014 study. The study, which was small (it was conducted on only 30 women), found that taking vitamin D supplements reduced levels of perceived pain over 50 weeks.

If you're struggling with fertility issues, some science indicates that vitamin D might help. A presentation at the European Congress of Endocrinology in 2017 suggested that some testing could be done on the link between low vitamin D levels and fertility in men and women; if that link turns out to be confirmed in later studies, vitamin D could be an easy way to help fertility issues.

A study in 2016 found that in mice who had metabolic syndrome, vitamin D supplements appeared to positively affect their gut microbiomes, or the collection of bacteria that helps our digestive system work. Metabolic syndrome is a collection of conditions that increase susceptibility to type 2 diabetes, stroke, and other illnesses. It's not known yet whether this effect happens in humans too, but a 2018 study found that around one third of American adults have metabolic syndrome, so it could be a very vital step in treating a common issue.

By the time millennials start to enter retirement, they may have a new range of vitamins available to help. Whey protein supplements, usually associated with gym bros, have been discovered in a study in 2017 to help muscle repair in elderly men. It's not known if this applies to elderly women or to younger people, though.

A 2010 study found that where you keep your vitamins is important: storing them in humid places like the bathroom or kitchen, where a lot of steam is a regular occurrence, can degrade their efficiency and ingredients. Keep them in a dry, cool place.

One of the issues with vitamins is that they aren't subject to rigorous regulation by the FDA. A 2013 study found that the amounts of vitamin D actually varied a lot between different pills and producers, so it's not always confirmed that you're absorbing what you're guaranteed on the bottle.

Vitamins interact with one another — and a study in 2018 found that vitamin D absorption is actually pretty inefficient when you don't have enough magnesium in your diet. "People are taking Vitamin D supplements but don't realize how it gets metabolized. Without magnesium, Vitamin D is not really useful or safe," the co-lead of the study, Professor Mohammed S. Razzaque, said in a press release. Low magnesium levels might be hampering the effectiveness of your vitamin D pills.

Folic acid has a solid reputation for helping the health of pregnant people and their growing babies, but it may also help general health long-term. The National Health Service reports that a large study in China discovered that long-term use of folic acid appeared to reduce the risk of stroke and cardiovascular illness. It's just one study, so more work needs to be done to replicate the findings.

B vitamins — the collection of vitamins including B-5 and B-12 —  are necessary for many elements of our health. A study in 2017 found that adding vitamin B-complex supplements to antipsychotic treatment for people with schizophrenia helped to reduce their symptoms.

Eating too much vitamin C, whether in your diet or in supplements, is an actual thing. Harvard Health explains: "In some people, high doses — more than, say, 2,000 or 3,000 mg per day — can cause symptoms such as diarrhea, nausea, heartburn, gastritis, fatigue, flushing, headache, and insomnia. People with chronic liver or kidney conditions, gout, or a history of calcium-oxalate kidney stones should take no more than 1,000 mg a day." It's very difficult to reach this level of vitamin C over-saturation, but if you're on very high levels of vitamin C for a long period of time, check with your doctor.

The Mayo Clinic has noted that both vitamin E and vitamin A have been linked to health issues if taken daily in people who don't require it for medical reasons. Both were linked to a higher risk of premature death, as was beta-carotene, which is converted into vitamin A in the body. Talk to your doctor about any supplements you take.

Calcium supplements can help with bone health if you're not getting enough calcium in your diet for some reason, but Harvard Health notes that they've been linked to health issues. Calcium taken in supplements, as opposed to vitamins absorbed from milk products and other foods, have been found to heighten the risk of kidney stones and heart attacks.

Why do some people react differently to others when it comes to vitamin supplements? An interesting study in 2019 may provide the answer; people taking vitamin E were found to react differently because of their genetics. Vitamin E supplements haven't had a reputation for efficiency, but this study indicates a possible reason why: some people may simply not be genetically primed to absorb the supplements, so the pills haven't helped. It remains to be seen whether this applies to other kinds of vitamin supplements too.

A 2019 study found that taking nutritional supplements doesn't help prevent depression in people who are classified as overweight and at-risk of mental health issues. It was the largest study of its kind, and looked at vitamin supplements over a year — and there was no change in the risk of depression.

As we understand more about vitamins and how our bodies absorb them, future supplements may use different methods to try to help. An artificial antioxidant called TEMPO is currently being examined as the next go-to supplement, and it's possible that other supplements of the future will involve gut microbes, genetic coding or other personalized features to make them more effective.

Taking a multivitamin every day is a nice routine, but you may not be getting exactly what the product promises. If you feel as if you may have a vitamin deficiency, it's a good idea to see your GP to talk about dietary options and other possibilities first.