Summer Heat, Winter Freezes and Vitamin D
Heat can be a killer. In the US, more than 1,250 and 700 deaths were attributed to heat waves in 1980 and 1995. High temperatures baked Europe in June. Excessive heat, and cold, also keeps people indoors. Without direct exposure to sunlight, vitamin D cannot be synthesized by our skin and the prevalence of vitamin D deficiency can increase.
In the absence of sunlight, the only solution to maintain serum 25(OH)D concentrations is to consume foods containing vitamin D. The primary food sources of vitamin D are animal foods. Schmid and Walther review the vitamin D3 (cholecalciferol) content of animal foods. It isn’t great news. The highest vitamin D concentrations are found in fish liver. Offal is also a concentrated source of vitamin D. Unfortunately, not many people eat these options. Milk is a good source of vitamin D only if fortified. But at 120-125 IU per cup, it takes 4.8 to 6.4 cups of milk to meet recommended intakes for vitamin D (depending upon age). Fluid milk consumption is decreasing which makes us more dependent upon other animal food sources or dietary supplements.
Vitamin D deficiency is prevalent globally, as can be seen by the International Osteoporosis Foundation interactive map. Green indicates an optimal/desirable vitamin D status (>75 nmol/l), yellow is suboptimal (50-74 nmol/L), orange indicates insufficient (25-49 nmol/L) and red indicates severe vitamin D deficiency (<25 nmol/L).
Don’t be a vitamin D statistic. Have your serum 25(OH)D3 status evaluated, choose animal sources of vitamin D and supplement as needed. -mm-
Schmid A, Walther B. Natural vitamin D content in animal food products. 2013 Adv Nutrdoi:10.3945/an.113.003780