I heard vitamin D might prevent diabetes. Is this true?

If you are referring to type 1 (insulin-dependent) diabetes, you probably heard correctly. Animal studies suggest that vitamin D supplementation significantly represses the development of insulitis and diabetes and, furthermore, a vitamin D deficiency increases the onset of type 1 diabetes.1^,2 Human studies seem to support this as well. In Norway, a retrospective study showed that children who ingested cod liver oil—a rich source of vitamin D—had a significantly lower risk of type 1 diabetes.3

It is not clear how vitamin D works in modifying the onset of type 1 diabetes, but the vitamin is a potent modulator of the immune system and it may alter certain inflammatory- and immune-signaling agents associated with development of the disease. A recent review of the literature suggests that doses less than 400 IU daily may not reduce the risk for type 1 diabetes, but that doses of 2,000 IU a day (the tolerable upper intake level) may have a strong, protective effect.4

Because few foods naturally contain vitamin D, sunlight and supplementation supplies most of our vitamin D requirement. Vitamin D deficiency is also prevalent in infants who are solely breast-fed and do not receive vitamin D supplementation.5

I know that fish oils are good for my heart, but I was told I should also consume fish to protect my bones. Is there any truth to that?

Many people are familiar with the literature that omega-3 fatty acids may reduce the risk of heart disease, diabetes and some cancers. Animal studies, and now recent human studies, suggest a role in bone health as well, particularly in relation to omega-6 fatty acids. A long-term study in California tracked the ratio of dietary omega-6 fats to omega-3s in relation to bone-mineral density in middle- and older-age individuals. They tested BMD by dual-energy X-ray absorptiometry—the gold standard for assessing bone loss—and found that the higher the ratio of linoleic acid (omega-6) to alpha-linolenic acid (omega-3), the lower the BMD. These results were independent of age, body mass index and various lifestyle factors.6

The ratios creating problems were in the range of 7-to-1 and 8-to-1 of omega-6s to omega-3s. Foods high in omega-6 (or with a high omega-6 to omega-3 ratio) are corn, safflower, sunflower, soybean and cottonseed oils. One of the best sources of omega-3 is fatty, cold-water fish such as salmon. The best vegetarian source is flax oil. In addition, walnuts, pumpkin seeds, canola oil (I recommend cold-pressed and unrefined), and some dark, leafy green vegetables such as kale, spinach, purslane, mustard greens and collards do have some omega-3s.

Will coffee raise my blood pressure?

Experience demonstrates that there are individual responses to both coffee and caffeine, which is also found in tea, chocolate and herbal supplements such as guarana (Paullinia cupana). We all know that some people will be wired on half a cup of joe, whereas others can fall asleep after three cups. Therefore, it doesn?t surprise me when some people seem to have blood-pressure sensitivities to coffee and others don?t.

Recently, a meta-analysis of both coffee and straight caffeine compared 16 randomized, controlled studies involving more than 1,000 subjects.8 When the researchers looked at blood pressure and coffee (with an average daily intake of 725 ml, or about three cups per day), they found that there was a very minimal rise in blood pressure (1 mm Hg systolic, less than 1 mm Hg diastolic). When they looked at studies of just caffeine and blood pressure, they found that the rise, although modest, was clearly more evident (410 mg a day of caffeine produced a systolic increase of 4 mm Hg and a diastolic increase greater than 2 mm Hg).

So is it the coffee or caffeine? The coffee trials didn?t clarify how much caffeine there was per cup. Caffeine varies by variety, brewing method and other factors, but one could estimate that a cup of brewed coffee might average 75 mg to 100 mg of caffeine, so those three cups of coffee might equate to 225 mg to 300 mg of caffeine. Since there was a clear increase in blood pressure with the caffeine trials, it does seem that caffeinated coffee raises blood pressure—though generally not a lot—and it?s certainly variable in its effects. Decaffeinated coffee is unlikely, in most people, to have much consequence on blood pressure.

Dan Lukaczer, N.D., is director of clinical research at the Functional Medicine Research Center, a division of Metagenics Inc., in Gig Harbor, Wash.

References
1. Zella JB, et al. Oral administration of 1,25-dihydroxyvitamin D3 completely protects NOD mice from insulin-dependent diabetes mellitus. Arch Biochem Biophys, 2003;417(1): 77-80.
2. Zella JB and DeLuca HF. Vitamin D and autoimmune diabetes. J Cell Biochem, 2003;88(2): 216-22.
3. Stene LC and Joner G. Use of cod liver oil during the first year of life is associated with lower risk of childhood-onset type 1 diabetes: a large, population-based, case-control study. Am J Clin Nutr, 2003;78(6): 1128-34.
4. Harris SS. Vitamin D in type 1 diabetes prevention. J Nutr, 2005;135(2): 323-5.
5. Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr, 2004;79(3): 362-71.
6. Weiss LA, et al. Ratio of n-6 to n-3 fatty acids and bone mineral density in older adults: the Rancho Bernardo Study. Am J Clin Nutr, 2005;81(4): 934-8.
7. Simopoulos AP. Evolutionary aspects of omega-3 fatty acids in the food supply. Prostaglandins Leukot Essent Fatty Acids, 1999;60(5-6): 421-9.
8. Noordzij M, et al., Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials. J Hypertens, 2005;23(5): 921-8.