Our results, along with previous work by other groups, may indicate the need to consider age as an independent risk factor for secondary hyperparathyroidism, and also serve as confirmation of existing recommendations for higher vitamin D intake in older adults (Holick et al., 2011), as preventing PTH increase in them may require higher levels of vitamin D. It should be noted that at higher VMR values, which include the range of vitamin D deficiency, no association of PTH and age was noted, indicating a more complex regulation of PTH production in these conditions. Here, PTH is linked to secondary hyperparathyroidism.