Blog

When daylight saving time ends on November 1 and evenings suddenly go dark before dinner, many people notice the same thing: less energy, more cravings, harder mornings, and a flatter mood. It happens even in sunny San Diego, and it is often more than just the time change.

Feeling tired in winter is usually driven by a combination of less daylight (which shifts your body clock and melatonin), lower vitamin D, and in some people, underlying thyroid or hormone imbalances that become more noticeable when days are short. Mild seasonal dips are common, but persistent fatigue, low mood, weight gain, or brain fog deserve testing rather than just pushing through. At Quantum Functional Medicine in Carlsbad, we look at thyroid function, hormones, and key nutrients together to find the cause.

Key takeaways

• Less morning light disrupts your circadian rhythm, which affects sleep, energy, and mood.
• Vitamin D levels tend to fall in winter, even in Southern California.
• Low thyroid function, low testosterone, and perimenopause can all mimic or worsen winter fatigue.
• Seasonal affective disorder (SAD) is a recognized form of depression that usually starts in late fall.
• Lab testing helps separate normal seasonal changes from a treatable imbalance.

Why does winter make you tired?

Your energy is tied to light. Morning sunlight helps set your internal clock, shuts off melatonin, and supports serotonin, a brain chemical involved in mood. When days get shorter, many people wake in the dark and spend most daylight hours indoors. The result can be later, groggier mornings, afternoon slumps, carbohydrate cravings, and lower motivation.

Is it seasonal affective disorder or just winter blues?

Winter blues are mild and do not interfere much with daily life. Seasonal affective disorder (SAD) is a type of depression that follows a seasonal pattern, typically starting in late fall or early winter and easing in spring. Common signs include:

• Low mood most of the day, nearly every day
• Oversleeping and trouble getting up
• Craving carbohydrates and gaining weight
• Losing interest in activities you usually enjoy
• Pulling away from friends and family

SAD is less common in sunny climates but still happens here, and symptoms deserve real support. Light therapy, counseling, and in some cases medication are established treatments. Our clinic also offers interpersonal psychotherapy (IPT) for mood support.

What role does vitamin D play?

Your skin makes vitamin D from UVB sunlight, and the amount of UVB reaching the ground drops in winter. Combine that with indoor jobs and sunscreen, and many people head into winter low. Vitamin D supports immune function, muscle strength, and bone health, and low levels are associated with fatigue and low mood. A simple blood test tells you where you stand, so supplementation can be dosed correctly instead of guessed.

Could it be your thyroid?

Hypothyroidism and Hashimoto's thyroiditis cause fatigue, feeling cold, weight gain, dry skin, constipation, and brain fog, which are easy to blame on winter. Standard screening often checks TSH alone. A functional workup may also include free T4, free T3, and thyroid antibodies for a fuller picture. Read more in our article on functional thyroid treatment.

How do hormones affect winter energy and mood?

Hormone shifts can amplify seasonal symptoms:

• Perimenopause and menopause: falling estrogen and progesterone can disrupt sleep, mood, and energy. See our BHRT guide for perimenopause and menopause.
• Low testosterone in men: fatigue, low motivation, reduced strength, and low mood. See our article on low testosterone symptoms and testing.
• Cortisol: holiday stress and poor sleep can leave you wired at night and exhausted in the morning.

What can you do about winter fatigue?

1. Get morning light: 10 to 30 minutes outside soon after waking, or a 10,000-lux light box if mornings are dark.
2. Keep a steady sleep schedule: same wake time every day, even after the clock change.
3. Move daily: outdoor walks give you light and exercise at the same time.
4. Eat for steady energy: protein at every meal and fewer refined carbs to blunt cravings.
5. Test, then supplement: check vitamin D, iron, B12, thyroid, and hormones rather than guessing.

Winter energy and hormone care in Carlsbad

If you are dragging through the darker months, our Carlsbad clinic can help identify whether nutrients, thyroid, or hormones are part of the picture and build a plan for patients across North County San Diego. Request a consultation to get your labs reviewed.

Frequently asked questions

Why am I more tired after daylight saving time ends?

The clock change shifts light earlier in the morning and darker earlier in the evening, which can temporarily disrupt your circadian rhythm. Most people adjust within a week or two. Lingering fatigue may point to another cause.

Can you get seasonal affective disorder in Southern California?

Yes, although it is less common than in northern climates. Shorter days, indoor routines, and individual sensitivity to light can still trigger seasonal mood changes in San Diego.

What labs should I check for winter fatigue?

Common tests include vitamin D, a complete blood count, iron and ferritin, B12, a thyroid panel (TSH, free T4, free T3, antibodies), blood sugar, and sex hormones when symptoms suggest an imbalance.

Do light therapy lamps work?

Bright light therapy, typically 10,000 lux for about 20 to 30 minutes in the morning, is an established treatment for seasonal affective disorder. Ask a provider before starting if you have eye conditions or bipolar disorder.

When should I seek help right away?

If low mood includes thoughts of self-harm or hopelessness, seek help immediately by calling or texting 988, the Suicide and Crisis Lifeline, or going to the nearest emergency room.

This article is for educational purposes only and is not medical advice. Please consult a qualified healthcare provider to determine whether testing or treatment is appropriate for you.