When your hair isn't behaving the way it usually does, the first instinct is to look at your products. But some of what shows up in your hair starts somewhere else entirely, and fall is when two nutrients in particular are worth a closer look: vitamin D and iron.
Both are easy to run low on without realizing it, both can show up in how your hair looks and feels, and both can be checked with a simple blood test. Here's what to know about each one as the days get shorter.
Why Vitamin D Drops in the Fall
Most of your vitamin D doesn't come from food. Your skin makes it when sunlight hits it directly. That works well in summer, but as fall sets in, the days get shorter, the sun sits lower in the sky, and you spend more time indoors and covered up.
In much of the country, the sun gets too weak to do the job for months at a time. In a city like Boston, for example, your skin can't make enough vitamin D from sunlight for about four months of the year. And sitting by a sunny window doesn't help, because the glass blocks the part of sunlight your skin needs.
The vitamin D your body stored over the summer has to carry you through those months, and for a lot of people, it runs out before spring.
Why Skin Tone Matters
This part rarely makes it into hair care conversations, and it should. Melanin, the pigment that gives skin its color, works like a natural sunscreen. That protects deeper skin from sun damage, but it also means people with darker skin make less vitamin D from the same amount of sunlight. Someone with deep brown skin may need far more time in the sun to make the same amount of vitamin D as someone with lighter skin.
Put that together with shorter fall days, and it's easy to see why low vitamin D is so common, especially for women of color living in colder parts of the country. Many people have no idea their levels are low until they're tested.
What Vitamin D Has to Do With Your Hair
Vitamin D plays a role in the hair growth cycle, and researchers have found links between low vitamin D and some types of shedding. What isn't clear yet is whether low levels cause the shedding or simply show up alongside it. Either way, if you're noticing more hair in your comb this fall and you rarely spend time in direct sun, your vitamin D level is worth knowing.
Low vitamin D can show up in other ways too, like feeling tired, achy, or run down. But it often causes no obvious signs at all, which is why a blood test is the only way to know for sure.
Iron: The Other Nutrient Worth Checking
Iron helps your blood carry oxygen throughout your body, including to your scalp. It's one of the most common nutrients for women to run low on, and low iron is one of the best-known nutrition-related causes of shedding in women.
You're more likely to run low if you:
- Have heavy periods
- Are pregnant or recently gave birth
- Eat little or no meat
- Donate blood often
Common signs of low iron include feeling tired all the time, looking paler than usual, cold hands and feet, brittle nails, and getting winded more easily than you used to. Increased shedding can be part of that picture.
Here's the detail most people miss: a standard blood count can come back normal even when your iron stores are running low. Fortunately, a test called ferritin measures how much iron your body has stored, so if you're asking about your hair, ask your doctor to include it.
If you want to eat more iron, our guide to foods that support stronger hair has a list of iron-rich options. One tip that isn't on it: save your tea and coffee for between meals rather than with them, since both can make it harder for your body to absorb iron from food.
Why You Shouldn't Just Start Taking Supplements
It's tempting to grab a bottle of vitamin D and a bottle of iron and call it handled. Both can cause problems when you take more than you need, though. Too much iron can build up in your body and become harmful, and very high doses of vitamin D taken over time can cause serious side effects.
A blood test takes the guessing out of it. It tells you whether you're actually low, and if you are, your doctor can recommend the right amount for you and recheck your levels later. That's a much better plan than adding supplements and hoping.
Your Hair Care Routine Still Matters
Getting your vitamin D and iron where they should be supports your body from the inside, and your hair care routine takes care of the outside. Keep up your moisture, handle your hair gently, and look after your scalp. If you're building out that routine, our Hair Growth Collection is a good place to start.
Shorter days are a good reminder to check in on yourself, not just your hair. A quick conversation with your doctor and a simple blood test can answer questions that no product on your shelf can.
Frequently Asked Questions
Can low vitamin D cause hair loss?
Researchers have found links between low vitamin D and some types of shedding, and vitamin D plays a role in the hair growth cycle. It isn't yet clear whether low levels directly cause shedding, but if you're seeing more hair fall out and rarely get direct sun, it's worth having your levels checked.
Should I take vitamin D or iron for my hair?
Not without checking first. Taking more of either than you need can cause problems. A blood test tells you whether you're actually low, and your doctor can recommend the right amount if you are.
What blood tests should I ask for?
Ask for a vitamin D test, often listed as 25-hydroxy vitamin D, and a ferritin test, which measures your iron stores. A standard blood count can look normal even when your iron stores are low, so ferritin is the one to make sure is included.
Can I get enough vitamin D from the sun in the fall and winter?
In much of the country, not reliably. The sun is often too weak for months at a time, your skin can't make vitamin D through a window, and deeper skin tones need more sun exposure to make the same amount.
Why are women more likely to be low in iron?
Periods, especially heavy ones, and pregnancy both draw on your iron stores. Women who eat little or no meat are also more likely to run low, since iron from plant foods is harder for the body to absorb.
