During the winter months, reduced hours of sunlight can be associated with seasonal symptoms of depression, which can vary in duration and intensity. Some people experience symptoms concerning enough to meet criteria for a condition known as seasonal affective disorder (SAD). This type of depression is characterized by a recurring seasonal pattern, with symptoms typically beginning in the late fall and early winter and lasting until spring or summer. Not all seasonal mood changes constitute SAD, which can only be formally evaluated and diagnosed by your healthcare provider.
According to the American Psychiatric Association, an estimated 5% of U.S. adults experience SAD. The causes of SAD are not fully understood, though one theory is that lower vitamin D levels in winter may potentially contribute to symptoms. But how much of a role does vitamin D really play in seasonal depression?
Exploring the link between vitamin D and seasonal mood changes
Vitamin D is a nutrient found in some foods, but your body also produces it in response to sunlight exposure. This vitamin is essential not just for bone health, but it also supports your immune system, nerves and muscles.
The active form of Vitamin D works like a hormone. Research suggests it may help regulate serotonin, a chemical messenger in the brain that affects mood. Since vitamin D levels tend to be lower in winter when there is less sun exposure, this could reduce serotonin activity and may play a role in seasonal depression.
Understanding vitamin D and immunity
Studies also suggest a potential link between low Vitamin D levels and risk of upper respiratory illnesses like colds and flu. So, interestingly, vitamin D may play a role in supporting immune function. Though the research is not conclusive, it indicates that if your vitamin D levels dip in winter, it may be harder for your body to fight off bugs going around. It’s easy to imagine how getting repeated colds could worsen any seasonal depression symptoms you may already be experiencing.
Signs of vitamin D deficiency
Many people with low vitamin D don't notice any symptoms. However, possible signs of a vitamin D deficiency in adults may include:
- Fatigue
- Bone pain
- Muscle weakness
- Mood changes (e.g., depression)
Since these symptoms are non-specific and may be associated with a wide variety of health conditions, it’s important to discuss any new changes in your health or mood with your healthcare provider.
Low levels of Vitamin D are common, especially in winter at far northern or southern latitudes, but lack of sun exposure is just one possible reason for low vitamin D. Deficiency can also happen if certain medical conditions (e.g., celiac disease, Crohn’s disease, cystic fibrosis) or medications (e.g., laxatives, steroids, cholesterol-lowering medication) interfere with your body’s ability to properly absorb or metabolize vitamin D.
The role of vitamin D testing
Since low levels may not always cause noticeable symptoms, getting your vitamin D measured with Labcorp OnDemand's Vitamin D Test can help assess if you have a deficiency. Labcorp OnDemand also offers a Vitamin Deficiency Test, which evaluates your levels of vitamins B12 and B9 (folate) in addition to vitamin D, as well as a Micronutrient Test that measures blood levels of vitamin D, vitamin B12, folate, magnesium, iodine and zinc.
If your healthcare provider confirms you have low vitamin D, they may recommend supplementation and/or lifestyle changes to help get your levels back up. However, research indicates that vitamin D supplementation alone is unlikely to be an effective treatment for seasonal depression. So, it is important to consider a variety of management strategies with guidance from your healthcare team.
If you think you may be dealing with symptoms of depression, don't hesitate to talk to a healthcare provider or access treatment. You can also call or text 988 to connect with a trained crisis counselor at any time for confidential support. If you need assistance finding a healthcare provider or treatment, the National Institute of Mental Health offers several resources to help meet your needs.
