Winter is well upon us down under. When the cold and grey weather settles in, summer can feel like a distant memory and our moods can feel like they're riding a rollercoaster.

For some, SAD (which has been on a hiatus in the warmer months) can throw itself back into our lives. SAD is the acronym for Seasonal Affective Disorder, a form of depression that usually begins in autumn and continues through the winter months. It is believed to affect up to 10% of the population. Symptoms include feeling sad or anxious, fatigue, concentration problems, irritability and feelings of guilt and hopelessness.

The role of sunlight

Although the exact cause of SAD isn't clear, a number of studies suggest it may be triggered by lack of sunlight. One hypothesis is that reduced sunlight exposure interferes with the body's biological clock that regulates mood, sleep and hormones. A perhaps more compelling theory is the fluctuation in vitamin D levels with the changing seasons in response to the amount of sunlight. The sun plays a vital role in helping the body to absorb vitamin D.

"Vitamin D is activated through a reaction between UV rays and cholesterol in the skin," explains healthily's Nutritionist and Lifstyle Medicine Practitioner Jennifer May, "levels are typically at their peak during summer months, and drop off during winter which is when people are typically most at risk for a deficiency."

Why is Vitamin D important?

"Vitamin D regulates the immune system, helps with optimising cell differentiation (which is important for cancer prevention), helps the intestines absorb calcium and magnesium for strong muscles and bones, and helps to regulate mood through production of the neurotransmitters dopamine and serotonin." explains Jennifer, "A lesser known fact is that Vitamin D is actually a steroid hormone that plays a key part in regulating sex hormones for optimum fertility and virility."

Am I at risk of deficiency?

You may be at a greater risk of vitamin D deficiency if you stay mostly indoors for health, work or other reasons, have naturally dark skin, or avoid the sun for skin protection or due to medical reasons. Where you live is also a factor - our Tasmanian Medical Laboratory reports that 60% of Tasmanians present with a vitamin D deficiency at the end of winter.

Combating SAD - the Winter Blues

Here's what Jennifer has to say about boosting those vitamin D levels:

• Increase your exposure to sunlight, but be sure to follow safe sun guidelines - speak to your GP if you're not sure what's safe for you. Even if it doesn't look that sunny outside you can still get valuable Vitamin D, so do what you can to spend as much time outside and keep up regular exercise.
• Top up your vitamin D levels through dietary sources during winter - vitamin D rich foods include dairy products (particularly cheese), egg yolks, and oily fish such as tuna, mackerel and salmon. Many of us actually start to crave more of these foods during these colder months.
• Consider a vitamin D supplement - talk to your GP or pharmacist about which supplement may be right for you.

Concerned you may have a vitamin D deficiency? Finding out is easy with a simple blood test - see healthily's Vitamin D Check for more details.

Winter, SAD or whatever the reason - if you need help or know someone else who may, you can find the support needed at one of many helplines listed on Beyond Blue.

Adapted from a post originally published in May 2017 as 'Cracking the SADs'