What Does Vitamin D Do? 5 Questions Answered

When win­ter comes around, you might pre­pare by dress­ing in warmer clothes, stock­ing up on fire­wood, or get­ting your shov­el out of the back of the garage. 

These small steps can help you tack­le the cold win­ter months, but they shouldn’t be the only pre­cau­tions you take — espe­cial­ly when it comes to your health. 

Dur­ing the cold­est peri­od of the year, you are at greater risk for dif­fer­ent win­ter injuries, and health con­di­tions than at oth­er times dur­ing the year. One aspect of your health you may want to take into con­sid­er­a­tion is how much vit­a­min D you’re getting.


As the days get short­er and the tem­per­a­tures get cold­er — does your vit­a­min D lev­el get low­er like many peo­ple say it does? 

Here’s that answer and more to some of the vit­a­min D ques­tions you have but have nev­er got­ten a chance to ask.

1. What Does Vit­a­min D Do?

You may have heard the words vit­a­min D” but not know much about it. You know you need it, and you know it’s good for you, but you may not total­ly under­stand what it is or how it works.

In gen­er­al, vit­a­mins are a nec­es­sary part of your body’s abil­i­ty to func­tion and stay healthy. Vit­a­mins help your body’s cells grow, devel­op, and func­tion every day. There are 13 vit­a­mins that are con­sid­ered essen­tial, and vit­a­min D is one of them. 

Vit­a­min D is a fat-sol­u­ble vit­a­min, mean­ing that in excess it can be stored in your mus­cles, liv­er, or fat­ty tis­sue. Vit­a­min D helps your body absorb cal­ci­um, which is need­ed for healthy bones. A lack of vit­a­min D can lead to health issues like osteo­poro­sis in old­er adults or rick­ets in young children. 

2. How Do You Get Vit­a­min D?

There are two main ways you get vit­a­min D nat­u­ral­ly each day: in the foods you eat and through your skin, like being out in the sun.

When it comes to a vit­a­min like vit­a­min C you might know exact­ly what kinds of food and drink can help you get it. But vit­a­min D can be more confusing. 

You can get vit­a­min D in foods and drinks like:

  • Cheese
  • Egg yolks
  • Salmon, mack­er­el, tuna, and oth­er salt­wa­ter fish
  • Mush­rooms
  • Cere­als and milk which have vit­a­min D added to them 

You can also get vit­a­min D through sup­ple­ments that you can take each day, depend­ing on your needs. Your pri­ma­ry care provider can help you bet­ter under­stand whether a vit­a­min D sup­ple­ment is a good choice for you. Just like you might take a dai­ly vit­a­min, you can take a spe­cif­ic sup­ple­ment just for vit­a­min D. 

Your pri­ma­ry care provider can keep track of your vit­a­min D lev­els through rou­tine blood tests — that’s why it’s so impor­tant to make and keep your appoint­ment for your annu­al well­ness exam. Sched­ule yours today.

3. Do You Real­ly Need More Vit­a­min D in the Winter? 

When it comes to vit­a­min D and the long win­ter months, here’s the real ques­tion most peo­ple want answered: Do you need to take a vit­a­min D sup­ple­ment dur­ing the winter? 

It’s true that you might be at a high­er risk for vit­a­min D defi­cien­cy if you spend a lot of time indoors or live in a place where there is less sun­shine. And it’s also true that your vit­a­min D lev­els can drop through­out the win­ter months. One study showed that your vit­a­min D lev­els are high­est in Sep­tem­ber and low­est in March. 

With this in mind, win­ter can and does bring low­er lev­els of vit­a­min D for some peo­ple — but it’s dif­fer­ent from per­son to per­son. Many fac­tors, in addi­tion to how much sun­light you get, can impact your vit­a­min D lev­els, like your diet. Some peo­ple are at a high­er risk for vit­a­min D defi­cien­cy, and win­ter can increase this risk for those individuals.

4. Who Is at Risk for Vit­a­min D Deficiency?

You are at a high­er risk for vit­a­min D defi­cien­cy if you: 

  • Have a dark­er skin tone
  • Are old­er
  • Have a chron­ic health con­di­tion like celi­ac or Crohn’s disease
  • Have osteo­poro­sis, liv­er dis­ease, or kid­ney disease
  • Are obese or have had gas­tric bypass surgery
  • Take cer­tain med­ica­tions like anti-seizure drugs, anti­fun­gal drugs, and HIV/AIDS med­i­cines (among oth­ers) that impact your body’s abil­i­ty to uti­lize vit­a­min D

If you are at risk for vit­a­min D defi­cien­cy, you should talk to your Duly provider. They can give you options for dif­fer­ent ways to sup­ple­ment your vit­a­min D sup­ply dur­ing the win­ter months (or at any time of year) such as over-the-counter or pre­scrip­tion strength supplements.

5. What Can I Do if I’m Not Get­ting Enough Vit­a­min D?

Not get­ting enough vit­a­min D from the sun and the foods you eat can lead to neg­a­tive impacts on your health — but your Duly provider can help you under­stand your num­bers and take the next steps to bet­ter health. 


If you are curi­ous about your vit­a­min D lev­els and their effect on your phys­i­cal and men­tal health, talk to your pri­ma­ry care provider. With a sim­ple blood test (often con­duct­ed at your annu­al well­ness vis­it) your provider can see if you need more vit­a­min D and help you take the nec­es­sary steps to boost your levels.

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  • I am a family man at heart and believe family, community and personal connection play a huge role in shaping our health. Inherently curious, I listen to my patients and honor their experiences and perspectives with compassion to build lifelong partnerships. I use a hands-on, collaborative approach to empower my patients with the knowledge and tools necessary to navigate their lifestyles, health and well-being.