Many people suffer from symptoms known as SAD - seasonal affective disorder during the winter months. This is closely correlated with lack of sunlight exposure. Sunlight exposure can benefit mood by boosting levels of key hormones and also by producing vitamin D. Vitamin D is produced in the liver and kidneys from precursor chemicals that are synthesized in the skin, when UV rays from the sun shine on it.
What sunlight does.
Sunlight boosts levels of the important mood hormone serotonin. This is almost certainly the key effect when considering mental health. Serotonin improves mood, and reduced levels of it are found in people who suffer from SAD - seasonal affective disorder. It is thought that serotonin developed in bilateral animals (animals with a left and right hand side) as a way to respond to their environment. If they could find food and resources in one direction, say left, they would release more serotonin and feel happier. This would encourage them to carry on seeking food in that direction. It is interesting to note that depression is often treated with drugs called SSRIs or selective serotonin reuptake inhibitors, which attempt to boost levels of serotonin in the brain by preventing serotonin being removed.
Sunlight is thought to boost levels of dopamine. Dopamine is associated with intense pleasure, such as a sexual climax, that piece of music that makes you shudder, good food and recreational drugs. So having increased dopamine levels should make you feel more euphoric and this is likely to be the pleasure we feel when we open the windows on a sunny spring morning.
Sunlight suppresses the release of the hormone melatonin. Melatonin controls our sleep cycles with more inducing sleep and less being associated with wakefullness. It also plays a role in the regulation of female menstrual hormones.
Creates vitamin D
Sunlight creates vitamin D in the form of cholecalciferol when it hits our skin. Cholecalciferol can also be taken up from the diet. Once in the body the cholecalciferol called vitamin D3 is converted by the liver into calcidiol, the form that is measured in tests for blood levels of vitamin D. It may then be further converted by the kidneys into calcitriol, which is the most potent form of the vitamin. You can see from this that kidney disease could cause problems related to vitamin D deficiency.
What vitamin D does.
Vitamin D receptors are present in most of the tissues of the body, including the brain. This is indicative that it has a broad range of effects. It is not surprising therefore that low levels of vitamin D are associated with many different disorders. As far as the brain goes, vitamin D deficiency has been shown in studies to be directly linked with depression. The presence of vitamin D receptors in the cortex and hippocampus areas of the brain also imply it should improve memory and cognition. Several studies have indeed found this to be the case, and especially in depressed patients. There is also evidence that apart from its effects on mood, higher blood levels of vitamin D are also associated with a number of other health conditions.
Better survival rates from various forms of cancer. This is probably due to its ability to stop cancer cells from dividing to form more cancer cells and to change back into ordinary cells of the body.
Protection from autoimmune conditions such as multiple sclerosis, rheumatoid arthritis, type 1 diabetes as well as the skin condition, psoriasis. It also boosts levels of antimicrobial proteins and as such is associated with better immunity to colds and flu.
Lowers blood pressure
Lower blood pressure as it naturally inhibits the kidney enzyme renin, which controls the creation of angiotensin II, a protein that constricts arteries.
Protects the bones
Protection against osteoporosis due to vitamin D's role in absorbtion of the bone mineral, calcium from the intestines.
Yes vitamin D can actually make you faster! It has been found to increase the amounts of fast twitch fibres in your muscles and studies have linked it to quicker reaction times, muscular strength and better balance. All this without any training.
Some natural vitamin D sources are shown above and left. Oily fish such as fresh tuna, mackerel, sardines, pilchards, salmon and trout are particulalry good sources as is liver. Finding vitamin D in other foods is a hit and miss affair as it is either present in small amounts or as fortification of processed foods. Only by reading a label, or by knowing more about the food in question can you be sure how much vitamin D you'll be eating. With eggs it would depend on whether the chickens had a vitamin D rich diet. Vitamin D should be taken with foods containing fat as it is a fat soluble vitamin and will not be absorbed well without fats being present.
Treatment of SAD.
To improve mood try: http://www.philips.co.uk/c/light-therapy/38702/cat/
Vitamin D supplementation has also been shown to improve mood in some people. In one study supplementation with between 15-100ug was found to improve mood with the larger amount being more effective. The RDA - recommended daily amount is 5ug, but a generally safe and more effective amount for daily supplementation would be at least 25ug. In fact a single large dose of vitamin D is normally pretty safe also. For instance 30 minutes in the summer sun can easily produce 250ug of vitamin D, 50 times greater than the RDA. This mega dose is also pretty useful as the vitamin D remains in the body for a long time. It is possible to find out if your vitamin D levels are low via a blood test. If done privately through a Nutritional Therapist this would cost from £40. For most people supplementation will be safe to do, but if somebody is taking the following drugs: (Cholestyramine (Questran), colestipol (Colestid)), orlistat (Xenical), mineral oil, and Olestra) they should avoid it.