Folate network genetic variation, plasma homocysteine, and global genomic methylation content: a genetic association study

Table 1 Characteristics of Normative Aging Study participants, 1961-2001, with measurements on three phenotypes.

	Plasma homocysteine^a	Global genomic DNA methylation (Alu elements)^b	Global genomic DNA methylation (LINE-1 elements)^b
	N = 760	N = 628	N = 621
Age at phenotype measurement	68.6 (7.3)*	72.5 (6.8)	72.5 (6.8)
Education - college graduate or higher (%)	26.8	28.6	28.7
White (%)	100	100	100
Baseline BMI (kg/m²)	25.9 (2.9)	25.9 (2.9)	25.9 (2.9)
Cigarette smoking^c
Current (%)	6.7	5.4	5.5
Former (%)	63.0	63.4	63.5
Never (%)	30.3	31.2	31.1
Alcohol intake (% consuming ≥ 2 drinks/day)	12.4	13.7	13.5
Baseline diabetes diagnosis (%)	0.13	0.16	0.16
Baseline systolic blood pressure (mm Hg)	122.1 (12.7)	121.7 (12.5)	121.6 (12.6)
MTHFR 677 C>T (rs1801133) TT genotype (%)	12.2	12.3	12.6
Plasma folate (ng/ml)^d	10.4 (5.7)	17.2 (15.1)	17.0 (14.9)
Plasma vitamin B-6 (pmol/ml)	84.9 (85.3)	104.6 (96.1)	104.8 (96.7)
Plasma vitamin B-12 (pg/ml)	458.9 (190.6)	512.8 (371.2)	514.9 (373.8)
Plasma total homocysteine (nmol/ml)	10.6 (3.7)	11.0 (4.2)	10.9 (4.2)
Global DNA methylation in Alu elements (%)		26.3 (1.1)
Global DNA methylation in LINE elements (%)			76.9 (1.9)

*mean (standard deviation) unless otherwise indicated
^aN for homocysteine group ranges from 730 to 760 for variables in table.
^bMen in the two global genomic methylation groups were very similar, and dates of marker collection were nearly identical. N for Alu group ranges from 618 to 628, and N for LINE-1 group ranges from 611 to 621.
^cSmoking status was assessed using most recent data prior to phenotype measurement.
^dHomocysteine and corresponding plasma folate, vitamin B-6, and vitamin B-12 data were collected prior to the initiation of folate fortification; global genomic methylation markers, and corresponding plasma nutrient markers were measured post-folate fortification, in a later time period.

ISSN: 1471-2350