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The sun is a pretty big deal. It sustains life on earth and can provide a good base tan—just remember to apply SPF. But unfortunately, dreary winter weather makes it harder to catch a good amount of rays, which can affect your mood, sex life, and—you guessed it—sleep cycle. 

According to the journal Environmental Health Perspectives, lying out in the summer sun for just half an hour helps your body produce over the daily recommended amount of vitamin D (though exact measurements depend on your skin tone). And all that D keeps your bones strong; supports healthy immune function; and helps calcium, magnesium, and vitamin K to best absorb, says Erin Stokes, N.D., medical director at MegaFood.

While it’s still possible to be exposed to the sun’s rays in fall and winter, Stokes suggests including alternative ways to help maintain your vitamin D levels. “I recommend getting your levels tested if you sense they’re low,” says Stokes. “Many people choose to supplement with vitamin D from October through April and consume food sources of vitamin D, like fatty fish—such as salmon, tuna and mackerel—cheese, and egg yolks. You can also find foods fortified with this vitamin, such as milk, orange juice, and cereal.” But if you’re not exactly sure what happens to your body when you don’t get enough sunlight, don’t worry, we got you. Here are the symptoms you should look out for. 

After One Day

Good news is: You have nothing to worry about if you don’t get enough sunlight after one day. According to integrative family medicine physician Bindiya Gandhi, your body won’t be affected. So if you decide to go a day without leaving your home, no need to feel guilty about it.

After One Week

However, after one week, you can expect to see some negative symptoms. “You’ll probably feel a little more lethargic and down, but not extremely depressed,” says Gandhi. When we get closer to the winter months or when there are consecutive days of rain or cold weather, most times, people will begin to naturally feel bad, and it’s because they’re not getting all those natural endorphins they normally would when they’re outside in the sun.

After One Month

Less exposure to sunlight can also cause a hormone imbalance. “When certain people don’t get enough sun, their neurochemicals get out of balance, and that can lead to serotonin going up, and then they become depressed. And where dopamine is supposed to make you happy, that slowly goes down,” says Dawn Cutillo, natural hormone specialist and author of The Hormone Shift. It can also cause an imbalance of progesterone and estrogen and erode testosterone, which can cause feelings of depression.  

“If you’re not exposed to sun long-term, it will affect your sleep cycle and our melatonin production, which will make you more depressed and forgetful, and you won’t be sleeping well,” says Gandhi. “And if people are experiencing SAD (seasonal affective disorder), this might be the time where they might want to discuss medication or therapy options.”

Experts agree that it’s important to try to rectify the situation ASAP, especially during the winter months, whether it’s through the use of a SAD light, taking a short walk in the middle of the day, or partaking in light therapy. Find something that works for your lifestyle to get your body’s chemistry back on track. 

After Six Months

Once you hit the six-month mark, your mood and energy levels will be at an all-time low.  During this time, you’ll begin to experience extreme depression and chronic fatigue, where it could affect your cognitive function and the way you interact with people,” says Gandhi. “Things like brain fog, forgetfulness, and chronic stress will occur all the time.” 

With the lack of sun over time, you also could experience an extreme case of vitamin D deficiency. “There’s a strong link between vitamin D deficiency and depression. The lack of it can cause inflammation and weaken your immune system,” says Gandhi. While all of this sounds scary, don’t fret. If you eat enough food with high sources of vitamin D, take an afternoon walk every once in a while, and maybe even consider a supplement after talking with a doctor, your body will be back to normal in no time. 

See more wellness: What Happens to Your Body When You Drink Enough Water What Happens to Your Body When You Walk 10,000 Steps Every Single Day What Happens to Your Body When You Sit for Long Periods of Time