The authors of this paper decided to check whether the content of selected minerals in human hair is projected into the nutritional status of the body expressed as the BMI. The study focused on evaluating the content of calcium, sodium, potassium and magnesium in the hair of 7845 individuals in relation to their BMI. 5126 women and 2719 men aged from 18 to 92, domiciled throughout Poland, were involved in the study. Hair samples were taken from several points of the occipital scalp. Ca, Na, K and Mg in the hair were determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The content of Ca and Na in the hair of obese people (>30.0 kg·m2) was higher (323 mg·kg−1 and 180 mg·kg−1) in comparison with the groups of people with normal body weight and those grade 2 underweight (<16.9 kg·m2): 191 mg·kg−1 and 103 mg·kg−1 respectively. The highest level of K (317 mg·kg−1) was found in the hair of people classed as grade 2 underweight. The body mass index caused no differentiation in the content of Mg in hair. Positive correlations were found between Ca-Na, Ca-Mg and Na-Mg and between the BMI of the subjects and the content of Ca in hair (R = 0.163; p < 0.01) and between the BMI and the content of Na (R = 0.191; p < 0.01). On the other hand, a negative relation between K and the BMI was correlated only to an infinitesimal degree (R = −0.030, p < 0.01). The results point to a relationship between the body mass index and the content of Ca, Na and K in the hair of adults