Vitamin D and the Winter Blues

This was a request from Bibil: Why do we feel depressed during winter?

Winter blues, called SAD for Seasonal Affective Disorder, is a seasonal depression and mood variation known to be related to how much sunlight you receive. Your mood is influenced by a complexed relationship between sunlight, melatonin (sleep hormone) and serotonin (awake AND good mood hormone).

Winter Blues 

As the dark hours increase during winter, our body increases levels of melatonin, leaving less hours for the body to increase its serotonin levels. Whereas during summer, serotonin levels increase when you are exposed to bright light making you feel in a better mood!

Indeed it is well known that bright light therapy can bring quick benefits to people with depression or SAD because light affects the balance between melatonin and serotonin

What's up with Vitamin D then?

Lights actually stimulates the production of a component called cholecalciferol, which the body eventually transforms into vitamin D (named D because it was the 4th vitamin discovered). It is the vitamin D that helps the body maintain higher levels of serotonin during the winter.

Which means that exposing your body to the sun (ie ultraviolet-B) during summer helps store this cholecalciferol for the coming winter months.

Where do we get that vitamin D?

• Sunlight-induced vitamin D production in the skin accounts for about 80% of obtained vitamin D.

It is of course well known that exposure to the sun also increases risk of developing skin cancer, so in all cases, moderation and more time spent during the early hours of the sun are better than the leather-type skin!!

• Diet makes relatively small contribution but can be obtained for example from oily fish, eggs or sun-dried tomatoes. 

• We can also obtain vitamin D through vitamin-Do fortified food (in the US: milk and orange juice) though it has been shown that to correct our vitamin D levels, supplements seem to be the best.

Skin complexion and vitamin D production 

This production is particularly efficient in individuals with low levels of skin melanin.

Therefore, Evolution theory suggests that people who migrated to the North developed a fair skin complexion to efficiently synthesize vitamin D under conditions of less UV-B exposure. The inverse s true that people living in sunny regions have a skin with high melanin content which protects against sunlight-induced damage.

Vitamin D and disease 

• Depression: It is also true to develop depression when you suffer from a vitamin D-sensitive disease such as obesity, high blood pressure, heart disease, cancer, multisclerosis, kidney disease, rheumatism where it was find that vitamin D levels were lower than the healthy population.
• Obesity: Obese and overweight people have an increasek risk for vitamin D defficiency because they tend to absorb it in their fat stores, which prevents to be utilized in their blood. In this case, a study has shown that a daily intake of supplements was both safe and effective at improving vitamin D status.
• Diabetes: In the case for example of Diabetes, it has been shown that vitamin D supplementation improves glucose metabolism by reducing insulin resistance.
• Vitamin D was discovered in 1922 by McCollum as the cure for Rickets, a bone disease where softened bones lead to fractures and/or deformities. But even before McCollum, it was well known that sunlight was effective in preventing rickets. Note that vitamin D and calcium levels are related.

Conclusion

Next summer, store up your vitamin D precursor by exposing yourself to the sun a maximun BUT at reasonable hours --> so no sunburn, no dark skin from the damaging midday sun which would be more aggressive than the searched benefits!!