The contracted days come as part and parcel of this time of year and leave us short on sunlight. One important effect of sunshine is that it drives the body's production of vitamin D—a key nutrient. A combination of wrapping up for winter and a dearth of sunlight can leave us low in vitamin D. So what can be done to ensure we keep levels of this nutrient up at this time of year?
Besides sunlight, the other major source of vitamin D is our diet. Cod liver oil is a significant source of vitamin D. For more than a hundred years taking cod liver oil has been advocated for its ability to ward off rickets and to ease stiff and creaking joints.
The ability of cod liver oil to supply the body with vitamin D may have important implications for both body and brain. For instance, there is evidence from both test-tube and animal experiments that shows vitamin D has the ability to reduce the risk of the development and spread of cancerous tumors. Not surprisingly, studies show that increased sunlight exposure is associated with a decreased risk of several forms of cancer, including those of the breast, prostate, and colon. Vitamin D is also crucial for bone health and seems to help protect against multiple sclerosis.
Some research suggests that vitamin D deficiency may play a part in seasonal affective disorder (SAD) —sometimes referred to as "winter blues." In one study, just five days of treatment with vitamin D (at a dose of 400 or 800 IU per day) was found to improve winter mood [1]. Further evidence for the potential for vitamin D to alleviate SAD came from research in which individuals were treated with either 600 or 4000 IU of vitamin D each day for at least six months. Both dosages of vitamin D led to improvements in the participants' mood and general well-being, with those on the higher dose of vitamin D benefiting the most [2].
Cod liver oil, like other fish oils, is also rich in omega-3 fats. These come in two main forms: docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). A high consumption of these fats has been linked with a reduced risk of cardiovascular conditions such as heart attack and stroke. Omega-3 fats have a natural anti-inflammatory effect in the body, and there is some thought that this biochemical benefit may be part of the explanation for why cod liver oil can provide relief from conditions like osteoarthritis and rheumatoid arthritis. And like vitamin D, these fats also have benefits for the brain. DHA appears to be important for the structural integrity of the brain, while EPA seems to have a more important role in the day-to-day running of the brain. Omega-3 fats show promise in the prevention and/or treatment of many mental ailments including depression and dementia.
To get reasonable levels of vitamin D and omega-3 fats from cod liver oil one needs to take 1-2 teaspoons a day throughout the winter. Fortunately, cod liver oils that have been naturally flavored (often with lemon or orange) are now available and represent a good option for those who do not like the taste of plain cod liver oil.
References:
1. Lansdowne AT, et al Vitamin D3 enhances mood in healthy subjects during winter. Psychopharmacology (Berl). 1998; 135(4): 319-23.
2. Vieth R, et al. Randomized comparison of the effects of the vitamin D3 adequate intake versus 100 mcg (4000 IU) per day on biochemical responses and the wellbeing of patients. Nutrition Journal 2004; 3:8 http://www.nutritionj.com/content/3/1/8
Dr. John Briffa is a London-based doctor, author, and health writer with an interest in nutrition and natural medicine.
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