Most of the foods that contain vitamin D naturally have been taken off the menu of the American diet due to the belief that fats are harmful to your health. Since vitamin D is manufactured by animals, a strict vegetarian won't get any vitamin D from their food intake. Foods that are high in vitamin D are also very high in fat and cholesterol as well, and have therefore been for the most part "black-listed." These include pork lard, bacon, egg yolk, liver, caviar, butter, and raw milk. Americans have recently been responding to the claim that fats are healthy as long as they are omega-3 fats, which has fortunately brought fatty fish, such as sardines, salmon, and mackerel, back on the menu. A fantastic source of vitamin D is cod liver oil, which used to be routinely given as a natural vitamin supplement to children, and still is in many parts of Europe. But Americans seem to have unfortunately abandoned this practice. Several foods in the American diet have been fortified artificially with vitamin D, but many of these, such as cereals, orange juice, and non-fat milk, contain little or no fat, so it is mysterious to me how the fat-soluble vitamin D can possibly be properly distributed in the product or properly absorbed.
The lack of adequate dietary fat contributes to the metabolic syndrome in at least four ways: (1) vitamin D is only available in fatty food sources because it is a fat-soluble vitamin, (2) calcium uptake is more efficient when the calcium is consumed with dietary fats, (3) calcium uptake depends critically on the presence of vitamin D, which is deficient due to (1) above, and (4) the burden of fat cells to manufacture fatty acids from sugar is alleviated by the dietary availability of fats from ingested food sources.
By far the best way to acquire adequate vitamin D is through sun exposure. Possibly one of the most important components of a healthy lifestyle is to spend ample time outside in the sunlight. However, today's lifestyle in America often leaves little time for outdoor activities. Furthermore, Americans have been trained to fear rather than bask in the sun, mainly due to the aggressive ad campaigns of the sunscreen industry arguing that the sun causes cancer. Of course, one needs to avoid sunburn, but, building up exposure slowly by developing a tan in the spring affords natural protection from burning in the summer. This strategy is, in my view, far preferable to liberally applying sunscreen. Sunscreen at an SPF level of 8 or greater effectively wipes out any opportunity to manufacture vitamin D in the skin. The protection acquired from all cancers due to the vitamin D that is manufactured in the skin upon sun exposure more than compensates for any increased risk to skin cancer caused by sun exposure.
Another healthy choice is to eliminate 'empty carbs' as much as possible. This includes such foods as cookies, donuts, candies, and soft drinks. Switch from white to whole wheat bread, and from white rice to brown rice. When eating potato, be sure to put lots of butter and/or sour cream on it. Potato ingested with fat has a much lower glycemic index than potato ingested without fat. This practice will help prevent blood sugar levels from spiking, which is healthy in terms of combating diabetes and heart disease. However, fixing the metabolic syndrome caused by high blood sugar is only possible if, along with limiting consumption of empty carbs, you also repair your deficiencies in calcium and vitamin D.
I would also argue that one should make sure to ingest adequate amounts of dietary fat, especially dairy fat . Whole milk is particularly outstanding because it contains substantial amounts of calcium and vitamin D, and it contains the necessary fat to assure that these two elements will be well utilized rather than just passing through the digestive system unabsorbed. Animal fats such as bacon are good sources of vitamin D, while also supplying fatty acids to help with energy needs. Fatty fish such as salmon and sardines are particularly good because they contain both omega-3 fats and vitamin D. One should assiduously avoid the trans fats found in processed foods such as cookies, crackers, and margarine. Butter and eggs are also healthy choices. Egg yolk is particularly good because it contains both fats and vitamin D. Nuts, particularly walnuts, almonds, and macademia nuts, are excellent sources of omega 3 fats.
Finally, it is essential to get enough calcium. Ingest the calcium with dietary fats. If you're fond of milk and cheese, then you can probably supply all of your calcium needs through dairy products, as long as you choose ones that contain fat (i.e., avoid non-fat dairy products). If you don't like milk or are allergic to lactose, then bean curd is an excellent choice for calcium. Bean curd can be prepared in lots of ways, from raw soybeans to soy milk to Chinese tofu dishes. However, it's not standard fare in the American diet, so it might be preferable to go with the third option for calcium, which is to eat lots of leafy green vegetables such as spinach, broccoli, kale, and mustard greens. Again, these need to be eaten with fats to be properly absorbed, which means frying them in oil or liberally adding butter.
It has been amply demonstrated in research studies that most vitamins and minerals taken in pill form are far less effective than the forms found naturally in foods. In many cases, you may be just wasting money on something that passes through the digestive system unabsorbed, and also creates abnormal situations of anomalously high levels of concentrated nutrients in the gut, which seems intuitively to be a bad idea. However, sometimes due to lifestyle constraints, it may be impossible to get enough sun exposure, and a vitamin D suppplement would likely be beneficial in such situations.