levels of vitamin D supplementation. Neither 25OHD nor calcitriol passes readily into breast milk.
With respect to the effects of vitamin D supplementation on serum levels of 25OHD in the infant, several studies have examined supplementation of infants with 300 or 400 IU of vitamin D per day, which raised levels above 75 nmol/L (Hollis and Wagner, 2004; Basile et al., 2006; Wagner et al., 2006); however, administering supplements of 300 to 2,000 IU/day to the lactating mother did not increase serum levels of the infant (Greer et al., 1982; Rothberg et al., 1982; Ala-Houhala, 1985; Ala-Houhala et al., 1988; Greer and Marshall, 1989; Hollis and Wagner, 2004). However, very high doses of vitamin D (4,000 to 6,400 IU/day) given to the mother have been reported to raise infant serum 25OHD levels (Hollis and Wagner, 2004; Wagner et al., 2006). As described by the authors, the work was a pilot study and involved 19 subjects. Specifically, when 4,000 IU of vitamin D per day was given to the mothers, the mean serum 25OHD level of the infants exceeded 75 nmol/L; with a dose of 6,400 IU/day, the serum 25OHD level of all infants exceeded this value. However, the functional impact of raising infants’ serum 25OHD levels above 75 nmol/L by increasing maternal dietary intake to such high levels is not clear, and the small sample size of this pilot study (n = 19) precluded conclusions about safety. One RCT found no benefit in raising infants’ serum 25OHD level above 50 nmol/L relative to measures of weight, length, and skeletal mineral content (Chan et al., 1982). Other work with the administration of high dosages of vitamin D to the mother has not specifically reported any functional health outcome to the breast-fed infant other than increased serum 25OHD levels; the breast milk calcium content is unaffected (Hollis and Wagner, 2004; Wagner et al., 2006). The administration of 400 IU/day to the infant remains the American Academy of Pediatrics’ recommendation (Wagner and Greer, 2008).
Serum 25OHD levels do not appear to change significantly during lactation compared with non-lactating states, although this has been assessed in only two small studies (Kent et al., 1990; Sowers et al., 1998). Because 25OHD does not pass readily into milk, it is not lost to the mother via this route. One study (Cross et al., 1995) reported an increase in maternal serum 25OHD level post-weaning, and although calcitriol levels increased in two studies (Cross et al., 1995; Kalkwarf et al., 1997), they did not in another (Specker et al., 1991). Studies have generally shown that providing vitamin D to lactating mothers increased their serum 25OHD levels, but otherwise had no significant effect on maternal outcome parameters (Cancela et al., 1986; Okonofua et al., 1987; Takeuchi et al., 1989; Kent et al., 1990; Alfaham et al., 1995; Sowers et al., 1998) and in clinical trials (Rothberg et al., 1982; Ala-Houhala, 1985; Ala-Houhala et al., 1988; Kalkwarf et al., 1996; Hollis and Wagner, 2004; Basile et al., 2006; Wagner et al., 2006; Saadi et al., 2007).